Photo and recipe courtesy of Dairy Farmers of Wisconsin.
Heat large skillet or sauté pan over medium-high heat.
Add bacon and cook until browned and crispy.
Drain on paper towels; set aside.
Reserve 2 tablespoons of bacon grease in pan and return to heat.
Add onions and a pinch of salt and pepper.
Sauté onions for 5 minutes, stirring regularly.
Add 1 tablespoon water, stirring to deglaze pan; stir in any browned bits.
Remove onions to bowl. Return pan to heat and add 1 tablespoon butter and 2 tablespoons water.
Bring to simmer, add spinach and pinch of salt and pepper. Cook for 3–5 minutes to wilt spinach; remove spinach to a bowl.
Heat a grill or grill pan over medium-high heat. Split whole-grain baguettes.
Assemble sandwiches: on each baguette bottom, spread 1–2 tablespoons jam, 2 ounces limburger slices, spinach leaves, onions, 2 slices of bacon, and baguette on top, in that order.
Carefully turn the sandwiches over and butter the bottoms.
Place sandwiches, bottom-side down on hot grill, then butter the tops of the baguettes.
When bottom sides are golden and cheese starts to melt, carefully flip sandwiches and brown sandwiches’ tops, melting the cheese.