https://leitesculinaria.com/93757/recipes-berliners-jelly-doughnuts.html
INGREDIENTS
500 g unbleached all-purpose flour, plus more for the work surface
70 g granulated sugar, plus more for coating
18 g instant yeast
3 g fine sea salt or kosher salt
240 ml room-temperature milk (70°F to 78°F/20°C to 26°C)
5 tablespoons unsalted butter (70 g), at room temperature, beaten
2 large eggs
2 large egg yolks
1 teaspoon freshly grated lemon zest, preferably organic
10 ml vanilla extract
Vegetable oil, for the bowl, the baking sheet, and for frying
130 g raspberry jam
DIRECTIONS
Dump the flour, sugar, yeast, salt, milk, butter, eggs, egg yolks, lemon zest, and vanilla in the bowl of a standing mixer fitted with the paddle attachment. (The hook isn’t needed here since this is a rather loose batter.) Mix on low speed until smooth, 8 to 10 minutes. It may be necessary to add a touch more flour to form a smooth dough.
Turn the dough into a lightly oiled bowl, cover with plastic wrap, and let stand at room temperature until double in size, about 1 hour.
Line a rimmed baking sheet with parchment paper or waxed paper and lightly brush the paper with oil. Turn the dough onto a lightly floured countertop and divide it into 16 equal pieces. (Resist the temptation to make larger doughnuts as they’ll be tricky to fry properly until the inside gets cooked thoroughly before the outside is overdone.) Shape each piece into a round and then flatten it slightly between the palms of your hands. Place each round, seam side down, on the oiled paper. Let stand uncovered at room temperature until double in size about 1 hour.
Pour enough oil into a deep pot to reach a depth of 3 inches. Attach a candy or deep-fry thermometer to the side of the pot and heat the oil over medium heat until it registers 350°F (177°C). Line a large platter or baking sheet with several layers of paper towels. Dump some more sugar for coating the doughnuts on a plate or in a large brown paper bag.
Place a few of the doughnuts in the hot oil, being careful not to crowd them. Fry until golden brown on one side, about 1 minute. Turn and continue to fry until the other side is golden, 1 to 2 minutes. (Don’t worry if there’s a line of light-colored dough around the perimeter of each Berliner. This is the “soft spot” where you’ll insert the tip of a pastry bag to pipe in some jam.) Drain the cooked Berliners on the paper towels, roll them in the sugar while still hot, and repeat with the remaining dough, keeping an eye on the thermometer to make sure the oil stays at a steady 350°F (177°C), adjusting the heat as necessary.
To fill the still-hot Berliners, place the jam in a bowl and stir it thoroughly so that there are no lumps. (If it’s particularly chunky, you may want to purée it in a food processor.) Scrape it into a pastry bag fitted with a large plain tip. Insert the tip into the soft spot of each Berliner and squeeze about 1 teaspoon jam into the center of each doughnut. Serve immediately. (As if you could resist!)