Preheat to 325, spray donut pan with nonstick spray and wipe off excess.
Mix flour, cocoa powder, baking powder, and salt in small bowl.
Beat butter and sugar on medium high until light and fluffy (about 3 minutes).
Add eggs, mixing for 30 seconds in between each addition.
Add vanilla. Turn off mixer and scrape down sides. Mix on high for 15-20 seconds.
Turn mixer to low. Add 1/3 of flour mixture. Add 1/2 buttermilk. Repeat, ending with flour. Add red food coloring if desired.
Transfer donut batter to pastry bag fitted with a round piping tip. Pipe batter into pan, leaving a 1/4” of room.
Bake for 8-10 minutes, or until they spring back when gently touched. Let rest for 5-7 min, remove from pan.