Preheat the oven to 400°F. Lightly butter a large baking sheet.
Beat together in a large bowl until smooth:
Trim the ends and crusts from:
Cut the loaf into 8 thick slices. Carefully cut into one side of each slice to create a pocket that you can open with your fingers. Spoon or pipe an equal amount of the filling into each pocket. Mix together in a shallow bowl:
One slice at a time, soak the stuffed bread in the egg mixture until thoroughly coated but not falling apart and transfer to a plate before browning. Melt in a large skillet over medium-low heat:
Working in batches, add the stuffed bread and brown on both sides, adding more butter to the skillet as needed. Transfer to the prepared baking sheet. When all the stuffed slices are browned, bake until fragrant and golden brown all over, about 6 minutes. Serve immediately.