Cinnamon-coated custard donuts

Ingredients:

• 4 tablespoons unsalted butter
• 1 tsp vanilla extract
• 0.5 cups premium flour
• 0.5 cup instant mashed potatoes
• 1.5 cups of sugar
• 0.5 tsp salt
• 3 large eggs + 1 white
• 2 tablespoons ground cinnamon
• Vegetable oil, for deep-frying

Preparation:

1. In a medium saucepan, combine 1/2 cup water, butter, and vanilla; bring to a boil, stirring to melt the butter. Remove from heat and stir in the flour, dry instant potatoes, 1/2 cup sugar, and salt. Return the saucepan to medium heat and mix until the dough is stiff and pulls away from the sides of the pan, about 2 minutes. Transfer the dough to the bowl of a stand mixer or a medium bowl; cool for about 10 minutes.
2. Beat the dough on medium-high speed with a mixer fitted with a paddle attachment or a wooden spoon; add the eggs and egg whites one at a time, beating thoroughly after each addition. After the eggs are incorporated, beat for about 1 minute more, until the dough is smooth and glossy. Let it rest for 1 hour.
3. In a shallow dish, combine the remaining 1 cup sugar and cinnamon. Place a tall, heavy-bottomed saucepan over medium heat and fill it about a third full with vegetable oil; heat to 170°C (350°F) on a deep-fry thermometer. Use a small ice cream scoop to drop the batter into the oil (fry in batches).
   
   Note
   
   It is very important to drop the dough into the oil with a small ice cream scoop, not a tablespoon..
4. Fry, turning once, until golden brown, about 6 minutes. Using a slotted spoon, transfer the donuts to the cinnamon-sugar mixture and roll to coat completely. Serve warm.