European Kitchen - Meat and Mushroom Sliders

### Beef and Mushroom Sliders

#### Ingredients:- Burger buns- 1 kg ground beef- 4 onions- 300 g mushrooms- 2 tablespoons butter- 1 tablespoon oil- Salt and pepper- 1 tablespoon sugar- 1 teaspoon smoked paprika- ½ cup mayonnaise (for spreading on the buns)- Cheddar and mozzarella cheese- 3 tablespoons barbecue sauce- Additional butter (for spreading on top)