Zapiekanki

In a pan over low heat, melt 2 teaspoons of butter with 1 teaspoon of oil. Add the chopped onion and cook for about 5 minutes until it's soft and translucent. Stir in the mushrooms, then turn the heat to medium and continue cooking for another 5–10 minutes. You want the mushrooms to soften and all their liquid to evaporate. Add the garlic and cook for another 1–2 minutes, just until it's fragrant. Season with salt and pepper, then stir in the mayonnaise and take the pan off the heat.

Slice the cooled baguettes in half lengthwise and arrange them cut-side up on the baking tray. Spread the mushroom mixture evenly over each half, then top generously with cheddar, ham, kabanos, and mozzarella. Return the tray to the oven and bake for 8–10 minutes, or until the cheese is bubbly and has turned a lovely golden brown.

While the zapiekanki are baking, heat the remaining butter and oil in a separate pan over medium heat. Add the sliced onions and fry for about 5 minutes until they're soft and deeply golden. Remove them from the heat and set aside. Once the zapiekanki are out of the oven, pile on the fried onions, a few dill pickles (if you're using them), and a sprinkle of fresh chives. Finish with a zig-zag drizzle of ketchup over the top.