📖 Instructions

1. First, in a small bowl, proof the yeast. Combine the warm milk (around 110°F or 43°C), sugar, and active dry yeast. Give it a gentle stir and let it sit for about 5-10 minutes, until the mixture becomes frothy. This step ensures your yeast is alive and kicking—no one wants a flat croissant!
2. While the yeast is proofing, in a large mixing bowl, whisk together the flour and salt. I like to use a balloon whisk for this, really aerates the flour and gives the croissants a lighter texture. I always sift too, just to be sure.
3. Add the softened butter to the flour mixture. Using a pastry cutter or your fingertips (if you’re feeling adventurous!), cut the butter into the flour until the mixture resembles coarse crumbs. Don’t overmix—you want little pockets of butter that will create flaky layers later.
4. Next, add the sour cream and the proofed yeast mixture to the flour mixture. Mix until a shaggy dough forms. It might seem a little dry at first, but keep at it. I find that using a dough hook on my stand mixer helps, but you can absolutely do this by hand. If the dough is too sticky, add a tablespoon of flour at a time until it comes together.
5. Turn the dough out onto a lightly floured surface and knead for about 5-7 minutes, until it becomes smooth and elastic. The dough should be soft and pliable, not tough. If it's too tough, let it rest for a few minutes and then continue kneading. This is crucial for developing the gluten, which gives the croissants their structure.
6. Place the dough in a lightly oiled bowl, turning to coat all sides. Cover the bowl with plastic wrap or a damp kitchen towel and let it rise in a warm place for about 1-1.5 hours, or until doubled in size. I usually put mine in the oven with the light on—creates the perfect warm environment. Pro tip: make sure the bowl is big enough because you dont want a dough explosion!
7. While the dough is rising, prepare the filling. In a large skillet, melt the butter over medium heat. Add the chopped onions and cook until softened and translucent, about 5-7 minutes. Stir occasionally to prevent burning.
8. Add the mashed potatoes and cheese to the skillet with the onions. Season with salt and pepper to taste. Mix well to combine all the ingredients. Taste and adjust the seasoning as needed. Some people like to add a pinch of nutmeg for warmth, but that's entirely up to you.
9. Once the dough has doubled, punch it down to release the air. Turn it out onto a lightly floured surface and divide it in half. Roll one half of the dough into a large circle, about 12 inches in diameter. Use a pizza cutter or sharp knife to cut the circle into 8 equal wedges.
10. Place a spoonful of the pierogi filling at the wide end of each wedge. Roll the dough from the wide end to the point, forming a croissant shape. Repeat with the remaining dough and filling.
11. Place the croissants on a baking sheet lined with parchment paper. Brush the tops with the egg wash (one egg beaten with a tablespoon of milk). This will give them a beautiful golden-brown color. If you're feeling fancy, sprinkle some sesame seeds or everything bagel seasoning on top.
12. Preheat your oven to 375°F (190°C). Bake the croissants for 15-20 minutes, or until they are golden brown and cooked through. Keep an eye on them—ovens can vary. If they start to brown too quickly, tent them with foil.
13. Remove the croissants from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely. Serve warm or at room temperature. These are delicious on their own, but also great with a dollop of sour cream or a sprinkle of fresh dill.