Lay 2 good sized pieces of heavy duty foil crosswise to each other, then spray generously with nonstick cooking spray.
Place your onion slices more or less in a single layer in the center of the foil. Add 2 Tablespoons of butter -spaced out a bit - then top with sauerkraut. I like to kind of scatter the sauerkraut over the onions.
Arrange your sliced sausage over the onions and sauerkraut. Finally, arrange the still-frozen perogies on top, in a single layer.
Spray the tops of the perogies with a bit of olive oil, season with a little salt and pepper, to taste.
Fold the foil ends in, rolling to form a well sealed packet. (See photos in the post, for how I do it.)
Place the pierogi foil packets over your fire or on the grill, cook for 20 minutes. Once the time is up, remove from the heat and check to make sure they’re heated through.
I like to aim for 160 F when an instant read thermometer is inserted into the center of a few perogies. If they’re not warm enough for your liking, re-fold the packets and return to the fire for another few minutes.
The actual cook time will depend on your grill, the distance from the heat, and how you’ve assembled your foil packets.
Once they’re hot enough, open the packets, garnish with more sauerkraut, sliced green onions, parsley, fresh dill, and/or sour cream if desired and serve hot!