First, make the dough! Combine yeast, warm milk and 2 teaspoons sugar in the bowl of a stand mixer and stir to dissolve. Wait 10 minutes. The mixture should get foamy. If it doesn't, the milk is the wrong temperature or your yeast is dead. Try again!
Add 3 cups flour and the remaining sugar. Add eggs one at a time and mix with the paddle until it starts to come together. Then add salt and combine.
With the mixer on low, add the butter a little at a time, mixing until it's all incorporated. Switch to the dough hook and mix on medium speed for 5-10 minutes until the dough is smooth and shiny, adding flour as needed. You can also do this by hand!
Knead on a floured surface for 5 minutes until slightly tacky but not sticky, adding flour as needed.
Place the dough in a large bowl, cover and let rise in a warm place until doubled in size, about 2 hours. You can also slow rise in the refrigerator overnight. Bring to room temperature before using.
When the dough has doubled, punch it down and place on a lightly floured surface. Roll the dough out to ½ inch thick and cut out rounds using a 3-inch round cutter. Re-roll the scraps once to cut more. Place rounds on parchment-lined baking sheets about 1 inch apart. Cover loosely with plastic wrap or a towel and let rise in a warm place until puffy, about 1 hour.
When ready to fry, heat 2 inches of oil in a heavy-bottomed pot to 350 degrees F. Fry the sufganiyot in batches without crowding the pot, 1½-2 minutes per side, until deep golden and cooked through (about 190°F inside). Transfer to a wire rack set over paper towels and let cool.
Spoon the jam into a pastry bag fitted with a long filling tip or a medium round tip.
When the sufganiyot are cool enough to handle, poke a hole in the side or top of each one with the tip and squeeze in about 1 tablespoon of jam, until you feel it get heavier.
Dust generously with powdered sugar right before serving and eat up!!