In a small bowl, sprinkle the yeast on top of the warm water and allow it to rest for 5 minutes until foamy.
In a medium sized bowl, whisk together the flour, 2 TBSP of the sugar, baking powder, baking soda and salt. Cut in the cold butter with a fork or a pastry cutter. Your flour mixture should have pea-sized chunks and may resemble wet sand.
Whisk the egg white and milk into the yeast mixture. Slowly pour this into the bowl with the flour and knead to form a soft dough.
Turn the dough out onto a well-floured surface and knead for about 3-4 minutes. Cover the dough and allow it to rest for 15 minutes.
Roll the dough out into an approximate 8"x8" square. Using a pizza wheel or a knife, slice the dough in half. Then slice each half into thirds so you have 6 pieces.
Transfer the 6 pieces of dough onto a parchment paper-lined (or silicone mat-lined) baking sheet. Cover the dough tightly with oiled plastic wrap and allow it to rise in a warm place for 45 minutes.
Preheat the oven to 400 degrees F.
Sprinkle the donuts with the cinnamon and remaining 1 TBSP of sugar.
Bake in your preheated oven for 10-12 minutes or until the donuts are a light golden color.
Allow the donuts to cool. In the meantime, whisk together all the ingredients for the glaze. Sprinkle the cooled donuts with the glaze and top with colored sprinkles if desired.
Donuts are best consumed the day they are eaten but can be stored in an airtight container at room temperature for 1-2 days. They should be reheated in the microwave if you are eating them later.