1. Heat the olive oil or butter in a large skillet over medium heat. Add the diced onion and cook until softened, about 5 minutes. Stir in the minced garlic and cook for another 1 minute until fragrant.
2. Add the ground beef or turkey to the skillet. Cook, breaking it apart with a spoon, until browned and no longer pink, about 6-8 minutes. Drain excess fat if needed.
3. Stir in the smoked paprika, salt, and black pepper. Then add the drained diced tomatoes and beef or vegetable broth. Let the mixture simmer for 3-4 minutes to blend the flavors.
4. In a separate bowl, mix together the sour cream, shredded cheddar, and half of the mozzarella cheese.
5. Spray your crockpot with non-stick cooking spray. Layer half of the frozen pierogis on the bottom of the crockpot, then spread half of the meat mixture over them.
6. Spread half of the sour cream and cheese mixture on top of the meat. Repeat with the remaining pierogis, meat mixture, and cheese mixture to create two layers.
7. Cover and cook on low for 3-4 hours or on high for 1.5-2 hours. The pierogis should be tender, and the cheese bubbly and golden on top.
8. About 15 minutes before serving, sprinkle the remaining mozzarella cheese on top, cover, and let it melt.
9. Garnish with fresh chopped parsley if desired, and serve warm.

When I first made this, I was worried the pierogis would get mushy, but slow cooking them in layers keeps their texture just right. Plus, walking away from the crockpot while it works its magic is my favorite kitchen shortcut—especially when the counters are already a mess from breakfast and snack prep.