Preheat the oven to 400 degrees F. In a mixing bowl, combine all of the ingredients together except for the bread. Mix well. Season with salt and pepper. Spread the mixture over each half of bread. Place a parchment lined baking sheet and bake until golden and bubbly. Remove from the oven and cool slightly before slicing.
In the bowl of a food processor, fitted with a metal blade, combine the egg, mustard, garlic and lemon juice. Season with salt and pepper. With the machine running, add the oil in a steady stream until the mixture is pale in color and thick. Remove from the processor and refrigerate for 1 hour.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.