Grease the bottom and sides of a loaf pan.
In a large mixing bowl mix 1 1/2 cups flour, cocoa, yeast, sugar and salt for about 1 minute until mixed and sifted.
In a small pan heat milk and butter until butter has just melted - do not boil! Mixture should feel warm to the touch.
Add to the dry ingredients and beat for 2 minutes. Add egg and vanilla and beat until incorporated.
Add enough extra flour to knead the dough, about 1/2 cup at a time. If you have a dough hook attachment it is best to use it to knead the dough so you do not need as much flour, which will make the bread tough.
Knead for 6-8 minutes until dough is elastic. Knead in chocolate chips. Put dough into prepared pan.
Cover and let rise in a warm draft free place until doubled (about 45 minutes).
Preheat oven to 350 degrees. Bake loaf 35-40 minutes until done. I usually tap it on the top and if it sounds hollow it's done.