Chocolate Hot Cross Buns

approx 4 cups white bread flour
2 1/2 tsp active dry yeast
5 tbs cocoa
1/4 cup sugar
1 1/2 tsp salt
1 cup whole milk
2 large eggs, plus one for glazing
1/4 cup butter, melted then cooled
1 tsp vanilla
3/4 cup chocolate chips
white chocolate for piping
Heat milk to body temperature. Proof yeast in milk until foamy (about 10 minutes). Whisk in eggs, butter and vanilla. In a large bowl, whisk together flour, cocoa sugar and salt. Add milk mixture and bring ingredients together with a fork. Turn out onto a lightly-floured surface and knead 5-7 minutes to form a soft, elastic dough. When finished, incorporate chopped chocolate. Return dough to bowl, cover and allow to rise in a warm place for about 1 3/4 hours, until doubled.
Turn out dough. Divide and shape into 16 buns and place on a large Silpat-lined baking sheet. Cover and allow to rise until doubled. Cut crosses into the top of each bun. Brush tops with an egg beaten together with a little water. Bake in a 375F oven for about 18 minutes.
When buns are completely cool, pipe melted white chocolate into the marks made before baking.