In a big bowl, combine egg, instant dry yeast, warm milk, granulated sugar, vanilla extract, and salt. Mix thoroughly until the sugar dissolves with a mixer.
Add all-purpose flour, knead the dough for 15 minutes until the dough is smooth, and elastic then add butter and knead again until the dough is not too tacky, about 15 minutes with a mixer.
Cover it with a wet cloth or cling wrap so the dough won't dry out. Proof the dough for 45 minutes or until double the size.
Cut the parchment paper into 12x6 cm. Sprinkle flour on top of the parchment paper to prevent the dough from sticking when it will be fried.
Once the dough has risen, portion the dough of the donuts 40 g each.
Make a smooth ball shape, then flatten with your hand, and then cut using a donut mold.
Put it on parchment paper and proof it again for 15 minutes.
Heat oil in a pan on medium heat. Fry the donuts at 150°C or 300°F until both sides golden brown. Rest them in the cooling rack.
Combine milk, cocoa powder, and powdered sugar until mixed thoroughly.
Dip the top of the donut then roll it in a chocolate sprinkle.
Enjoy!