1 tbsp butter
1 cup onions, finely sliced
1 tsp kosher salt
1 lb petite peas
3 cups chicken stock (more if needed)
1 bay leaf
1 cup baby arugula
1 tsp truffle salt (or to taste)
For the sandwiches
1/4 cup mayonnaise
1 tsp lemon juice
1/2 tsp truffle oil
16 baguette slices
8 slices sharp white cheddar (1" by2")
1Melt the butter in a large sauce pan or medium soup pot over medium low heat and stir in the onion slices and the kosher salt. Cook slowly over medium low to soften, about 5-7 minutes. If the onion starts to brown too quickly reduce the heat.
2Add the peas, chicken stock and bay leaf and bring to a boil. Reduce the heat and simmer for 10-15 minutes or until the onion is completely soft. Stir in the arugula and remove from the heat. Let sit for 5 minutes, then puree with an immersion blender or in a food processor or upright blender. Whir in the truffle salt and taste, adjusting seasoning if needed. Keep warm until serving.
3Meanwhile, stir together the mayonnaise, lemon juice and truffle oil. Spread the baguette slices with the mayonnaise mixture and sandwich with the cheddar cheese. Now coat the outsides of the sandwiches with more mayonnaise mixture. You can prepare these one hour ahead and refrigerate until you are ready to finish the dish.
4To Serve: Heat a panini grill or heavy skillet over medium high heat. Add the mini sandwiches and toast, turning once until golden and the cheese is melted. Serve warm over glasses or small bowls of the pea soup.