The key to a tender top round roast is to cook it low and slow. In this case, 1.5-2 hours at 275 degrees F. The slower cook time helps infuse flavor into the touch cut of meat while it becomes an ultra-tender perfect roast. If you want to take an additional step to tenderize your top roast, try marinating it in buttermilk for 30 minutes to 2 hours. The acidity helps break down the meat, so it's extra tender. We don't recommend going longer than 2 hours because you risk losing the texture, and the meat might become too tender. (Yes, there is such a thing.)