Clear a little counter space and gather everything: pierogies (still frozen), sliced kielbasa, chopped onion, minced garlic, shredded cheese, sour cream, soup, butter, and spices.

Slice the kielbasa on the diagonal into roughly ¼–⅓-inch rounds for nicer presentation and more surface area to brown.

Finely chop the onion and mince the garlic so they melt into the sauce while cooking.

Grate the cheddar (freshly grated melts best) and measure the sour cream and soup into a bowl so they’re ready to mix.

Pro tip (prep): Keep the pierogies frozen — they hold their shape better that way in the slow cooker.

Heat a skillet over medium-high heat and add a splash of oil or a little butter.

Add the kielbasa in a single layer and let it brown without moving too much — 2–3 minutes per side — until the edges caramelize. Transfer to a plate.

In the same skillet, add the onion and a pinch of salt. Sauté 4–6 minutes until translucent and starting to brown. Add the garlic for the last 30 seconds and stir until fragrant.

If there are brown bits on the pan, you can deglaze with a tablespoon of water and scrape them up — they add flavor to the casserole.

Pro tip (browning): Don’t overcrowd the pan; a little space between slices helps them get crispy edges and deeper flavor.

In a medium mixing bowl combine the can of cream of mushroom soup and the sour cream.

Add the black pepper and smoked paprika, then whisk until smooth and fully combined.

Taste the sauce — if it feels too thick for easy spreading, whisk in 1–2 tablespoons of milk or broth until it’s spoonable but still creamy.

Pro tip (sauce): Whisk continuously to prevent lumps and get a silky texture.

Lightly grease the inside of the crockpot with nonstick spray or a little butter so the edges release easily.

Place half of the frozen pierogies in an even layer on the bottom (a gentle overlap is okay — you don’t need a perfect single file).

Scatter half of the browned kielbasa and half of the sautéed onions over the pierogies.

Spoon half of the creamy sauce evenly across the layer, trying to cover most pierogies (they’ll soak up the sauce as they cook).

Sprinkle about half of the shredded cheese over the sauced layer.

Repeat: another layer of pierogies, the remaining kielbasa and onions, then the rest of the sauce. Finish with the remaining cheese and dot the top with the butter cubes.

Pro tip (layering): Avoid stirring after you assemble — stirring too early can break the pierogies. Layering lets the flavors meld while keeping the texture intact.

Cover the crockpot and cook on LOW for 2½–3 hours or on HIGH for 1½–2 hours. Times vary a little by slow cooker model, so use the time ranges as a guideline.

Start checking at the lower end of the time range: carefully lift the lid and test a pierogi by pressing gently — it should be tender but still hold its shape and the filling should be hot.

If the casserole looks too watery near the end, remove the lid and cook another 10–20 minutes to let some liquid evaporate. If it’s looking dry, stir very gently and add 2–4 tablespoons of milk or broth.

Pro tip (cooking): Resist frequent lid-lifting — every time you lift the lid you add 10–15 minutes to cook time. Only check once toward the end to test tenderness.

When pierogies are tender and the cheese is bubbly, turn off the slow cooker and let the casserole rest with the lid slightly ajar for 8–12 minutes. This helps the sauce settle and makes serving neater.

Sprinkle chopped fresh parsley over the top, and if you like, add extra shredded cheese or a dollop of sour cream to each serving.

Serve straight from the crockpot with a big spoon — this goes great with a simple green salad or roasted veggies.

Pro tip (finishing): Letting it rest is the secret to a creamier, less runny finish — resist the urge to dig in immediately.