Skyrim:To Kill an Empire

Quick Walkthrough
#Travel to Solitude.
#Enter the castle using the Gourmet's letter.
#Cook the Gourmet's famous stew and poison it at the end.
#Escape when the Emperor dies.
#Return to the Sanctuary.

Detailed Walkthrough
This Soup Is To Die For
thumb|right|The Emperor's decoy tasting his last meal
After securing the writ of passage into the Emperor's service, the rest of the plan is ready to fall into place. Following Astrid's instructions, travel to Solitude with the poisonous herb she gave you and report to head of security, Commander Maro. Show him the writ you stole from the Gourmet to gain entrance to the castle. Maro will allow you to pass with no trouble (commenting on your clothing depending on whether or not you are wearing the chef's hat or clothes), telling you to report to the castle's chef, Gianna. When Gianna greets you, she is both nervous and excited at the prospect of working with the great Gourmet. If you have yet to don your chef's hat, she will direct you to one on the shelf; you cannot begin "cooking" until you are appropriately attired. Once you are ready, say, Enough! The Gourmet is here to cook, not talk! Let us begin.

Gianna flusters, ''"Oh! Yes, but of course. Ahem. The Emperor has requested your signature dish - the Potage le Magnifique. I've taken the liberty of getting it started. But the cookbook only says so much, and everyone makes the Potage differently. I would be honored if we could make it... the Gourmet's special way. The base broth is already boiled. We can get started right now. So... which ingredient should I add next?"

The Potage le Magnifique, as described in Uncommon Taste,'' consists of a basic recipe and more ingredients added based on the chef's inspiration. Thus, you now have four ingredients to select, at each stage there are three options: the normal, the strange, and her choice.

When you are finished don't forget to add your "special" final ingredient: 
"Oh? What is this, some kind of herb? Are you sure? The Potage tastes perfect as it is. Any other ingredient might..."

'''Now, now, Gianna. Who's the Gourmet here?

"Heh, I'm sorry. Of course. It's your most famous recipe, after all. All right then, your secret ingredient's been added. And if I may say so... it has been an honor, getting a chance to prepare a meal with, well... the best chef in the entire Empire. I'll carry the stew pot, and lead the way up to the dining room. I'm sure the Emperor and his guests are dying to meet you."

It is not necessary to poison the Emperor with the Jarrin Root, however, in order to successfully complete the quest—you may kill him any way you want.

The Last Supper
When the Potage is complete, follow Gianna into the dining room as she serves the food to the Emperor. Right before you go in, there is a copy of the Enchanting skill book Catalogue of Weapon Enchantments'' on the table to your left. The Emperor will be speaking to the diners and a noblewoman about his cousin's murder when you enter, while two Penitus Oculatus agents stand guard behind him. Gianna will serve the Emperor the meal you cooked and, regardless of the ingredients, he will compliment its amazing taste.

If you added the Jarrin Root, the Emperor will soon die a rather unspectacular death. If you didn't add the poison, the Emperor and his guests will continue to slurp their soup until you assassinate him, which is easy enough since he has only 1 health point. The guards will attack you upon the Emperor's death, and Gianna will attempt to defend you before fleeing, although this may be avoided by successfully sneaking as he dies.

Once the Emperor is dead, exit through the door opposite where you entered upstairs.

Betrayal
Once out the door it looks like you are home free. However, as you cross the bridge, you will be ambushed by Commander Maro and several of his agents. He reveals that the man you killed was a decoy. Maro explains that someone from the Dark Brotherhood betrayed you and revealed to Maro your plans to assassinate the Emperor. Maro agreed to allow the Brotherhood to continue its business in exchange for you. He then tells you that because the Dark Brotherhood killed his son he intends to go back on his word and wipe them out. He has sent his agents to attack the sanctuary already. As soon as the conversation with Maro begins, your bounty in Haafingar will be set to 1500, so the city guards will be on the lookout for you. Escape the city by following the tower's stairs to the very bottom and head to the Brotherhood Sanctuary. You cannot fast travel directly to the sanctuary, so the quickest option is to fast travel to Falkreath and head west. The quest ends when you reach the Sanctuary.

Notes
You will be blamed for the emperor's death even if you kill him in a stealthy way that would normally avoid incurring a bounty.
It's possible to cross the bridge without incurring a bounty. To do this, cast a Destruction spell with a large area of effect (e.g. Fireball) a couple of times in both the upper and lower doors across the bridge, and slowly walk across. You'll be stopped as if Maro was talking, but you'll quickly exit back out, not getting attacked by the Penitus Oculatus or getting the bounty. You can then easily leave. As long as you don't kill the men you won't get a bounty. You will need to leave the city by foot as the guards are scripted to be hostile, which prevents fast-travel. Killing any single Solitude guard undetected may remove the bounty.
If you do get a bounty, then, as long as the three Penitus Oculatus men are dead, you can remove the bounty using your Thane status or Thieves Guild association (provided you have them available). However, even if you are a Thane of Haafingar, you will not be able to remove your bounty using your Thane status if Solitude is still under Imperial rule (fixed in Unofficial Skyrim Patch 1.0).
You should remove all items you own or want from the sanctuary before completing this quest, or they may be lost. However, the Unusual Gem located in Astrid's room will still be available.
Maro will have different dialogue based on your equipment when you arrive. If you are wearing a Chef's Hat or Chef's Tunic, he will say "Your clothes... of course... I should have realized..." Otherwise, he tells you "You are not dressed as I had expected." Regardless, he allows you to pass.
If you are in the form of a werewolf or vampire lord while crossing the bridge, you'll automatically change back when Maro appears.
After the quest, the Emperor's Tower will still be freely accessible, both from the walkway escape exit and from the front door inside the castle courtyard.  However, the door to the dining hall will be permanently locked from both sides.  The tower is completely abandoned after this point, so you can take what you want without consequence.  Be aware that the whole place respawns, however, so it cannot be safely used as a house.
After you tell Gianna to add the jarrin root to the recipe, if you quickly enter your menu you can drop it from your inventory; this allows you to retrieve it later. The quest will continue and the Emperor will still die of poisoning.
According to the recipe that exists in the game, carrots are a part of the "basic broth" that Gianna has already prepared. Yet, she will not object or even mention it if you suggest to add carrots.

Bugs
 
 Setting the stage through console does not work, as the stage always remains 0. The cause of the bug is currently unknown, and the easiest way to overcome it is to skip the quest entirely. To do this, move to a location away from the Dark Brotherhood Sanctuary, and use the console commands   followed by  . This immediately starts you on the following quest.
 
 Their reference numbers are  ,   and  . The problem can be fixed on the PC by entering the console (press "~") and typing   followed by  , and then repeating for the other two numbers.
 
To fix this, load from the previous autosave before cooking the Emperor's last meal, and do not loot the Emperor's dead body.
 
To fix this, simply reload the last save.

Quest Stages