In a stand mixer bowl, combine warm milk, yeast, and sugar. Let sit for 5 minutes until foamy.
¾ cup whole milk, 2¼ tsp instant yeast, ¼ cup 50g granulated sugar
Add the egg, yolk, and black food coloring if using, and mix to combine.
1 large egg, 1 egg yolk, 1/2-1 tsp black food coloring
Add flour, black cocoa, salt, and espresso powder. Mix for about 2 minutes, then add in the softened butter.
2½ cups all-purpose flour, ⅓ cup black cocoa powder, ½ tsp salt, 1/2 tsp espresso powder, ¼ cup unsalted butter
Knead on medium speed for 8–10 minutes until the dough becomes smooth, elastic, and shiny black.
Shape into a ball, place in a greased bowl, cover, and let rise in a warm spot until doubled (about 60–90 minutes).