The ripeness of your avocados is key! They should be very soft and easily mashed for the best texture. If your kitchen is cold, place the dough in a slightly warmed oven (turned off!) or near a warm stove to encourage rising. For a richer flavor, consider adding a teaspoon of vanilla extract along with the sugar. To check for doneness, insert a wooden skewer into the center of the loaf. It should come out clean or with just a few moist crumbs attached. Let the brioche cool completely before slicing to prevent it from becoming gummy.