Special equipment: parchment paper; a frying thermometer; a pastry bag For the dough:
Line a large baking sheet with parchment and lightly dust with flour. In the bowl of a stand mixer fitted with the dough hook, stir together the flour, granulated sugar, baking powder, yeast and salt. With the mixer on low speed, add the milk and eggs. With the mixer still running, add the butter, one piece at a time until fully incorporated. Continue to mix on medium speed until the dough is elastic enough to pull apart thinly and still see through it, about 10 minutes. Turn off the mixer and allow the dough to rest, covered, 20 minutes.
On a lightly floured surface, roll the dough out to 1/2-inch thickness. Cut out with a 2 1/2-inch circle cutter and transfer to the parchment-lined baking sheet. Let sit at warm room temperature until pressing the dough leaves a light dimple, 45 minutes to 1 hour.
For the praline glaze: Whisk together the praline paste and confectioners' sugar with 4 ounces hot water until smooth. If too thick, add more water; if too thin, add more sugar. Set aside.
For the doughnuts: Fill a large Dutch oven halfway with oil and bring to 375 degrees F. Carefully drop several doughnuts into the oil and fry until deep brown, 1 minute, then flip and fry the underside, 1 minute more. Transfer cooked doughnuts to a rack and let cool completely.
Poke a hole in the center of each doughnut using a skewer. Fill the pastry bag with Nutella, then pipe about 1 ounce Nutella into each doughnut. Dip the top of each doughnut in the praline glaze then swirl the top with additional Nutella or drizzle with melted chocolate.