Combine Dry: In the bowl of a stand mixer fitted with the dough hook, combine flour, dry yeast, and granulated sugar. Mix briefly, then stir in the kosher salt.
Mix on low until a shaggy dough forms, then increase to medium speed and knead for 8 to 10 minutes until smooth and elastic.
First Proof: Cover the bowl with plastic wrap. Let the dough rise at room temperature for 1 to 2 hours, until doubled in size.
Shape & proof
Roll: Punch down the risen dough and turn it out onto a clean, floured surface. Roll out to a ½ inch thick rectangle.
Stamp: Using a 2-inch round cookie cutter, cut out dough rounds. Reroll scraps to stamp out remaining rounds.
Second Proof: Transfer dough rounds to a parchment lined baking sheet, cover loosely with a clean towel, and let rise for 30 minutes until puffy and doubled in size.
Fry & assemble
Fry: Heat 2 inches of oil in a Dutch oven or deep skillet to 180°C (350°F). Gently lower 3 to 4 dough rounds into the hot oil. Fry for 1.5 to 2 minutes per side, until golden brown with a pale white line in the middle.
Drain: Remove with a slotted spoon and place on paper towels to drain excess oil. Let cool for 5 minutes.
Fill & Dust: Make a hole in the side of each donut with a small knife. Pipe strawberry jam into the center using a piping bag, then dust heavily with powdered sugar before serving.
Notes
Flour: Weighing your flour on a kitchen scale gives the best results. If using measuring cups, spoon the flour into the cup and level it off with a knife instead of scooping directly from the bag.
Oil Temperature: Use a candy thermometer to keep the oil between 340°F–350°F (170°C–180°C). Too hot will burn the outside while leaving the middle raw; too cool will make the donuts greasy.
Brandy or Vodka: Adding a tablespoon of brandy or vodka to the dough helps reduce oil absorption while frying so the donuts taste light rather than greasy.
Smooth Jam: Use seedless, smooth jam or strain out fruit chunks before filling piping bags so the tip doesn't clog.
Best Enjoyed Fresh: Fried donuts are best eaten the day they're made. Warm leftovers in the microwave for 10 seconds to soften the crumb back up.