Step 2

Heat 2 tsp butter and 1 tsp oil in a pan over low heat. Cook the chopped onion for 5 minutes until soft. Add the mushrooms, increase to medium heat and cook for 5–10 minutes until soft and all liquid has evaporated. Add the garlic and cook for 1–2 minutes. Season, stir in the mayonnaise and remove from heat.

Step 3

Halve the baguettes lengthwise and place cut-side up on the baking sheet. Spread the mushroom mixture over each half, then top with Cheddar, ham, kabanos and mozzarella. Bake for 8–10 minutes until the cheese has melted and is golden.

Step 4

Meanwhile, heat the remaining butter and oil in a pan over medium heat. Fry the sliced onion for 5 minutes until golden and soft.

Step 5

Top the baked baguettes with the caramelized onion, dill pickles if using, chives and a drizzle of ketchup.