I look forward to ramp season each spring. These delicate wild leeks grow in wooded areas and have a beautiful onion-garlic flavor and brilliant green color. While they’re delicious pickled or added to pastas, I like them best blended into a béchamel sauce. They tint the sauce a spring green that’s indicative of the flavor packed inside. Here the sauce makes a decadent topping for a croque monsieur, France’s famous toasted ham-and-cheese sandwich. Served alongside a simple salad, it’s a perfect meal to welcome warming weather.
For the ramp béchamel: Bring the milk, cream and ramps to a simmer in a small saucepan over medium heat. Adjust the heat and simmer gently, stirring occasionally, for 2 minutes. Transfer the mixture to a liquid measuring cup and use an immersion blender to blend the mixture until fairly smooth.
Return the pan to the stove and melt the butter over medium heat. Sprinkle the flour over the melted butter and cook, stirring constantly, for about 1 minute. Add the warm ramp milk and stir constantly to incorporate, then continue to cook over medium heat, stirring frequently, until the mixture comes to a simmer and thickens, 2 to 3 minutes. Season the sauce with salt and pepper and set aside.
For the sandwiches: Preheat the broiler. Place a large ovenproof skillet over medium-high heat. Spread one side of each slice of bread with 1/2 tablespoon of mayonnaise and place mayo-side down in the hot skillet.
Spread 1/2 tablespoon mustard on the other side of each piece of bread and layer 3 to 4 slices of ham and 1/2 cup of cheese onto each of 2 of the slices. Top with one of the other toasted pieces. Reduce heat to low and continue to cook until the cheese is melty, 3 to 4 minutes per side.
Spoon béchamel generously over each sandwich, and top the sandwiches with the remaining cheese. Transfer the skillet to the oven and broil to toast the cheese and finish warming the sandwiches.
Meanwhile, for the salad: Toss the lettuce leaves, oil and lemon juice together in a medium bowl to coat. Season with salt and pepper. Serve the hot sandwiches immediately with salad on the side.