Caramelized Onion and Fontina Tartine

Instructions

1. Caramelize the onions
   Heat butter and olive oil in a large skillet over medium-low heat. Add the sliced onions and cook, stirring occasionally, for 35-40 minutes until deeply golden brown and very soft. Add a splash of water if the pan gets too dry.
2. Season the onions
   When onions are caramelized, stir in the thyme leaves, balsamic vinegar, sugar, salt, and pepper. Cook for an additional 5 minutes to allow the flavors to meld. Remove from heat and set aside.
3. Prepare the bread
   Preheat your broiler to high. Toast the sourdough bread slices until lightly golden. Remove from oven and rub each slice with the cut side of a garlic clove.
4. Assemble the tartines
   Spread each bread slice with whole grain mustard if using. Divide the caramelized onion mixture evenly among the bread slices, spreading it to the edges.
5. Add cheese and broil
   Top each tartine with sliced Fontina cheese. Place under the broiler for 2-3 minutes, until the cheese is melted, bubbly and slightly golden.
6. Garnish and serve
   Sprinkle with additional fresh thyme leaves. Serve immediately while hot and cheese is still melty. Pair with a simple green salad for a complete meal.