Heat milk on the stovetop to about 110° F. Be careful not to overheat your milk. If the milk is too hot it may kill the yeast.

Combine milk, sugar and yeast in the bowl of a stand mixer and let sit for 5-10 minutes until yeast begins to show signs of activity.

Add eggs, vanilla, salt and flour to the bowl and mix using the dough hook on medium speed until fully combined and the dough begins to come together around the hook (approx 2-3 minutes).

Slowly add butter, one tablespoon at a time, waiting until each is incorporated before adding the next. Once all butter is added, continue knead the dough with the dough hook for 2-5 minutes until dough begins to strengthen and looks smooth.

Remove dough hook and cover bowl with plastic wrap or a towel and set in a warm place such as inside an oven with the light turned on for 1.5-2 hrs.

Transfer the dough to a different bowl or leave it in the mixing bowl with plastic wrap and place in the refrigerator overnight.

The next day, cut out 3in x 3in parchment paper squares and place them on a baking sheet.

Remove dough from the fridge and turn out onto a floured surface.

Divide dough into 12-14 equal pieces and roll each piece into a ball by flouring your hand and moving the cut dough to an un-floured spot on your counter. Then cup your hand around the dough and move your hand in a circular motion until the dough forms into a tight ball.

Let donut balls proof on the counter uncovered for 2-2.5 hrs until doubled in size and fluffy.

PREPARE THE CINNAMON SUGAR TOPPING

Combine sugar and cinnamon in a small bowl and set aside.

Heat a large pot of oil (grapeseed oil preferred) to about 360-375° F.

Gently place each doughnut into the oil including the parchment squares. Fry until golden brown, approximately 1-2 minutes per side.

Cool each donut on a baking rack for about 20-30s then dip each side in cinnamon sugar topping and return to cooling rack. We fry 2-3 donuts at a time to make the process easier to manage.

In a stand mixer, add butter and mix on high until fluffy.

Slowly add confectioners sugar and mix until combined.

Slowly drizzle syrup in a little at a time and allow it to incorporate completely before adding more.

Add remaining ingredients and mix until smooth and desired consistency. Add more confectioners sugar for a thicker consistency as needed.

Add filling to a piping bag or ziplock with the corner cut open. Fill donuts immediately once cool.

Once donuts are completely cool, use a wooden spoon handle to make a hole in the side of each doughnut. Pipe filling into the hole of the donut until filling begins to overflow.

Eat immediately or refrigerate if not consumed within 1-2 days.