Pour the warm milk (~105-115F) in the bowl of a stand mixer or a regular bowl and sprinkle the yeast overtop. Allow it to sit for about five minutes, so that the yeast becomes active.
Add the eggs, butter, salt, cinnamon, vanilla, and sugar. Mix to combine.
Slowly add the flour to the mixture (about 1 cup at a time). Only use 4cups and save the other 1/2 cup on the side. Scrape the sides of the bowl as you go along to make sure the flour is being well combined.
At this point, switch to the dough hook if you have one, or lightly sprinkle a work area with flour and place your dough on it. Knead the dough with the hook for 5-7 minutes or by hand for 15 minutes. If the dough is still too sticky and not forming, add the remaining half a cup of flour a tablespoon at a time. You want the dough to be elastic and smooth. It should still be sticky enough that it sticks to the sides of bowl or your hands, but not sticky enough that when you unstick it, there are chunks of dough on the side of the bowl or on your hands.
In a separate large bowl, spray with cooking spray and transfer the dough into the bowl. Cover the bowl with a wet warm towel and let the dough rise for an hour so that it doubles in size.
While the dough is almost done rising, prepare the brown butter cinnamon and guava filling.