
In a small bowl, combine the yeast, milk, and 2 Tbsp of sugar. Leave to sit for 10-15 minutes, or until foamy.
Mix flour, salt, and remaining sugar in a stand mixer bowl. Add eggs, vanilla, and foamy yeast mixture. Mix until dough comes together, then knead for 10 minutes.
Add butter little by little until fully incorporated. Mix for another 5 minutes.
Transfer to an oiled bowl, cover, and place in the fridge overnight to rise.
Roll out dough to 1/2” thickness, cut out donuts, and let rise for 45-50 minutes.
Heat oil to 350°F (180°C). Fry donuts until golden brown, about 3-4 minutes, flipping halfway.
Toss warm donuts in cinnamon sugar mixture.
Best eaten fresh, but leftovers can be reheated in the microwave.