Combine flour, cream, 2 eggs, yeast, salt, and sugar in the bowl. Using a stand mixer fitted with a paddle attachment by adding ingredients and mixing on medium speed until a homogenous dough comes together.
Transfer dough to a large mixing bowl, cover tightly with plastic wrap, and let rise at room temperature until about 1 1/2 times its original size, about 2-4 hours.
Lightly flour dough and transfer to a floured work surface. Form into a large ball approx 9". Transfer the dough ball to a parchment-lined rimmed baking sheet, tucking the seam underneath. Cover with plastic wrap weighted down with a kitchen towel and set aside at room temperature for 1 hour.
Preheat oven to 450°F When ready to bake, beat remaining egg with 1 tablespoon of water. Brush egg mixture on top of each bun until evenly coated. Sprinkle with sesame seeds.
Bake until deep golden brown, 12 to 15 minutes.
To assemble the sandwich:
Cut the roll in half; remove some of the bread on the bottom portion.
Add a layer of refried beans, sour cream, guacamole, salsa, lettuce, mozzarella cheese, and pickled red onion.