Summarize:

Place the two ingredients in a medium saucepan and set it on the stove over medium heat. Cook, whisking frequently, until the mixture becomes smooth and thick. Cook the mixture for at least 5 minutes. Under-cooking it can result in lumps, which will negatively affect the quality of your final dough. Continuous whisking is key here. If you do not whisk the mixture well enough, it will never become smooth and appropriately thick. Failing to whisk the mixture thoroughly can also cause the flour to begin burning on the sides and bottom of the hot pan. Remove the saucepan from the heat. Allow the flour mixture to cool until it drops to a temperature just slightly warmer than room temperature. Depending on how hot the mixture became while you cooked it, you may need to wait as long as 30 to 60 minutes before it becomes sufficiently cool. If the mixture is too hot when you add the other ingredients, you may accidentally kill the yeast, which would mean that the dough would no longer be able to rise. Combine the liquid flour mixture with the remaining 4 cups (500 g) of flour, along with the butter, yeast, salt, sugar, and milk. Mix well until evenly combined. Use your hands or a sturdy mixing spoon to combine these ingredients. Continue mixing the contents of the saucepan until you can no longer identify any separate ingredient in the mix. Turn the dough out onto a lightly floured counter and knead until it becomes smooth and elastic in consistency. You may need to lightly flour your hands, as well, to prevent the dough from sticking to your skin. Kneading the dough can take as many as 5 to 10 minutes. Test the smooth dough by attempting to stretch out a portion of it. You should feel some resistance as you pull, but the dough should still stretch well. Drizzle the oil over the top of the dough. Knead it into the dough and continue kneading for another 4 to 5 minutes. The finished dough will have a glossier appearance than it did before you added the oil, but it should not feel notably oily when you touch it. Place the dough in a greased bowl and cover it with plastic wrap. Let it rise in a warm place for 1 to 2 hours, or until doubled in volume. You can encourage the process further by draping a damp dish towel over the plastic wrap. The added humidity can cause the dough to rise quicker.
Combine the water and 2/5 cup (50 g) flour. Let cool. Add most of the remaining dough ingredients. Knead until smooth. Add the oil. Let the dough rise.