Make the donuts: In a stand mixer fitted with a paddle attachment combine flour, yeast, sugar, and sea salt. In another bowl combine milk and vanilla extract. Slowly stream in milk mixture while mixer is on speed 2, or just until combined. Add yolks, one at a time, beating in-between each addition until incorporated. Add butter and beat until dough forms.
Change paddle for hook attachment. Knead dough until uniform, smooth and elastic, less than one minute. Transfer dough to a large bowl. Drizzle a bit of canola oil on top and rub around dough until it is oiled all the way around. Cover with plastic wrap and allow to rise in a warm, non drafty place for 6 hours or in refrigerator overnight.
Remove plastic wrap and turn out dough on a floured surface (bread flour or all-purpose work). Roll out to a 1/4 inch thickness. Using a 3 inch round cutter, cut out dough. Place on a pan sprinkled with a bit of flour and repeat. Cover donuts loosely with a bit of plastic wrap and allow to rise one more time, for about an hour, in a warm and non drafty place.
Fry the donuts: add 2 inches of canola oil into a dutch oven or a large, high-sided pot. Heat oil to 365-375F, no less and no more. Carefully pick up donuts and drop into oil, 3-4 at a time or enough to loosely fill half of the pot you are using. Fry until golden brown on both sides, about 45 seconds per side. Drain on paper towels and repeat with remaining dough.
Meanwhile, in a small bowl combine topping ingredients to make the Mexican Chocolate glaze. Set aside.
Assemble donuts: Once donuts are cool enough to handle, dip one side into Mexican Chocolate glaze and place on a wire rack to set. Once set, serve and enjoy!