In a bowl, combine 1/3 cup of flour with 1 1/2 teaspoon of brewer's yeast and 1/3 cup of milk. Let this pre-ferment rest, covered with a damp cloth, for 30 minutes. In a separate bowl, combine the cocoa powder, cane sugar, a pinch of salt, and the remaining flour. Add in the pre-ferment and knead; add 1 egg and finally the chopped butter. Knead until you obtain a soft, even dough that pulls away from the edges of the bowl. Let it rise, covered with a damp cloth, for 1 hour until it doubles in size. Butter 16-18 fluted silicone molds (2” diameter, 1.5” deep). Form balls of dough weighing about 1 ounce each; flatten them out slightly into a disc and place a chopped piece of white chocolate in the center of each; close up the dough and form balls by rolling the dough between the palm of your hand and the work surface. Place each ball of dough in the buttered molds and let them rise for at least 1 hour, covered with a damp cloth. Bake the mini brioches for 15 minutes at 350°F. Remove from the oven and let cool. Combine 3/4 cup of powdered sugar with a teaspoon of water to obtain a thick yet fluid glaze: when you lift up the spoon, it should fall in a ribbon. If needed, add a bit more water. Top each mini brioche with a teaspoon of glaze and garnish to taste with currants; decorate with multicolored ribbons like a present.