Combine the mustard and honey in a small bowl. Set the bread slices on a work surface and spread one side of each with the mustard mixture, dividing it evenly. Top 4 of the bread slices with the Brie, prosciutto, apple slices, and then the remaining 4 slices of bread, mustard side down.
Beat the eggs and allspice in a large shallow bowl.
Melt 1-1/2 Tbs. of the butter in a 10-inch nonstick skillet over medium-low heat. Dip both sides of two of the sandwiches into the eggs. Cook, covered, until the bottom sides are golden, about 3 minutes. Carefully flip and continue cooking, covered, until the other sides are golden, about 2 minutes. Transfer to a plate and keep warm. Repeat with the remaining butter and sandwiches. Cut the sandwiches in half, sprinkle with salt, and serve.
Serve with a simple frisée salad.
nutrition information (per serving):
Photo: Scott Phillips