In a small bowl, combine 1 cup whole milk, warm, 2 ¼ teaspoons active-dry yeast and ¼ cup sugar. Let it sit for 5-10 minutes until foamy. If kneading with a stand mixer combine the ingredients in the mixer’s bowl; if kneading by hand, use a large mixing bowl.
Whisk together 2 large eggs, ¼ cup unsalted butter, melted and ½ teaspoon salt in the bowl.
Add the yeast mixture with 2 cups flour and stir. Gradually add the rest of the flour, mixing until a dough forms. You might need to adjust the amount of flour slightly depending on your climate.
With the dough hook attached, knead until you have a smooth and soft, but slightly sticky dough, about 5-7 minutes. If kneading by hand, turn the dough onto a lightly floured surface and knead for 8-9 minutes, until it’s smooth and elastic. It takes some arm muscle and patience. Add a tablespoon of extra flour at a time if the dough is too wet, but be careful as it should not be too dry or stiff.
Place the dough in a lightly oiled bowl, turn around to grease it all, cover with plastic wrap or a clean kitchen towel, and let it rise in a warm place for 1.5 to 2 hours, until doubled in size.
Gently punch down the dough to release air. Transfer to a lightly floured surface and roll it out to about ½ inch thickness.
Use a heart-shaped cookie cutter to cut out donut shapes. You can re-roll the scraps and cut out more donuts.
Place the heart-shaped donuts on a baking sheet lined with parchment paper. Cover loosely with a clean kitchen towel and let them rise for another 30-45 minutes. They will puff but not double.
Heat enough vegetable oil in a deep fryer or large saucepan to get to about 3 inches; the amount will depend on the size of your pot. Heat it to 350°F (180°C). Use a thermometer to check the temperature. Have ready a cooling rack with paper towels beneath.
Carefully add the donuts in batches, 2 or 3 at a time (don't overcrowd the pot or they will bring the temperature down) and fry for 1-2 minutes per side, turning once, until golden brown.
Remove the donuts from the oil with a slotted spoon and place them on the wire rack to cool slightly.
While they're still warm, dust the donuts with powdered sugar and serve.