Make juicy, flavorful sausage smash burgers stuffed with caramelized onions and topped with melty Jarlsberg cheese, homemade pickles, and crunchy sprout slaw.
Make the pickles. Combine sugar, vinegar, and water in a sauce pot and bring to a boil. Remove from the heat and add cucumber slices. Refrigerate for an hour before use. The cucumbers will be tender yet still have texture.
Prepare the slaw. Combine Brussels sprouts, mayonnaise, and garlic paste in a mixing bowl; mix well and keep refrigerated until ready to use.
Caramelize the onions. Heat oil in a large skillet over medium heat. Add onions and butter, and cook on medium-low heat for 30 minutes, stirring often until the onions are tender. Drain and reserve excess butter to toast the bread slices. Set the onions aside or in the fridge until cooled.
Toast the bread. Heat 1 tablespoon of the reserved butter in the same skillet over medium heat. Toast 2 slices of bread until desired doneness; repeat with remaining ingredients and set aside.
Char the tomatoes. In the same skillet, heat the tomato slices until a slight charring occurs, and set aside.
Prepare the burger patties. Combine the sausage and caramelized onions in a mixing bowl. Divide the sausage mix into 4 equal parts and roll into individual round ball shapes.
Smash the burgers. Using the same skillet, smash the sausage into the skillet with a flat spatula until you have your desired thickness.
Cook. Cook over medium heat for 12-15 minutes or until the natural juices run clear.
Add cheese. Top with the shredded cheese and let it melt before removing from the skillet. You can cook the patties all in the same skillet or two at a time.
Assemble. Layer the burger between toasted bread with tomatoes, pickles, and slaw. Serve.