These Butternut Squash Ricotta Pierogi with Brown Butter Hazelnut Sauce are the perfect fall meal. The dumplings are stuffed with a slightly sweet ricotta butternut filling and then served with crispy hazlenuts and sage.
In a food processor, combine the flour, salt, milk, cold butter, and eggs and pulse until well combined, about 30 seconds. Add more flour, a tablespoon at a time, if the dough is too sticky. Add more milk, a tablespoon at a time, if the dough is too crumbly. (You may have to make the dough in two batches, depending on the size of your food processor.)
Transfer the dough to a floured surface and divide into four equal pieces. Wrap the dough pieces in a damp kitchen towel and set aside.
Whisk together all of the filling ingredients. Set aside until ready to use.
Working with two pieces of dough at a time, roll the dough into two rectangles that are about 1/8 in [4 mm] thick each. Lay one rectangle dough piece over the pierogi press, fill each pierogi indentation with 1 Tbsp filling and place the other dough rectangle directly over the top. Push a rolling pin over the dough to seal the dumplings and turn the pierogi press over so the pierogi fall out of the press, removing any excess dough. Continue with the remaining filling and dough.
Bring a large pot of salted water to a boil over high heat. Working in batches, add enough pierogi to fit in a single layer and boil until they float to the surface, 4 to 5 minutes. Remove the pierogi with a slotted spoon and set aside on a plate.
In a large nonstick skillet over medium heat, melt 1 Tbsp of the butter. Working in batches, toss in 12 pierogi or enough pierogi to fill the pan in a single layer. Cook, stirring often, until the pierogi are brown on all sides, 7 to 10 minutes. Toss the sage into the pan during the last minute of sauteing. Repeat with the remaining butter and pierogi. Serve immediately.
Serve with crushed hazelnuts, warm sage, and black sesame seeds.