Place muffin liners in a 12 cup muffin pan. Set aside.
Sift the flour, cocoa powder, and salt into a large bowl. Set aside.
In another large bowl, mix eggs and sugar with a handheld mixer on medium speed for about 3 minutes, or until very pale in color. Mix in vanilla.
On low speed, add about 1/3 of the dry ingredients, then 1/3 of butter. Continue alternating with the remaining flour and butter. Add the chocolate chips and mix to combine. The batter can be refrigerated up to one day.
Fill each muffin cup about 2/3 full. Place in the oven and bake for 20-25 minutes. When the tops look shiny and set(like a brownie), test one cake with a toothpick: it should come out clean but not dry.
Move the bouchons in their liners to a cooling rack. After a few minutes, invert the bouchons and let them cool upside down in their liners; then lift off the liners.
The bouchons are best eaten the day they are baked.
Invert bouchons and dust them with confectioner's sugar.