Preheat a waffle iron or other hot sandwich maker. In a small bowl, cream together the softened butter, oil, and salt. Spread about 1 teaspoon of the butter mixture onto 1 side of 8 slices of the bread with an off-set spatula. Place the bread, buttered side down on the cutting board. Layer the inside of each slice with cheese, prosciutto, and pears. Top with the remaining bread slices, and spread with the butter mixture.
Transfer to the waffle iron and cook in batches until golden brown and the cheese is melted, 2 to 3 minutes.
To make the salad: In a hot skillet, add the lardons and cook until the fat is rendered. Remove lardons from the pan with a slotted spoon and place on a paper towel-lined plate.
To the skillet with the fat, add shallots and saute. Add red wine vinegar and mustard and stir the dressing to emulsify. Add the chives and season with salt and pepper. Drizzle the dressing over the salad greens and season, to taste, with salt and pepper.
Remove sandwiches from the waffle iron and transfer to plates. Cut in half diagonally and serve hot. Plate with salad and garnish with lardons.