Preheat the oven to 350ºF. Line a cookie sheet with parchment paper or waxed paper.
In a food processor or blender, blend the egg and lemon juice together for 10 seconds. With the processor running, slowly pour in the vegetable oil through the feed tube. The mixture will thicken. Add the mustard, Tabasco, and salt, and pulse once or twice to blend well.
Spoon the mixture into a small bowl and add the cheese, pepper, and truffle oil. Mix well.
Cut each slice of bread diagonally into two triangles. Spread about 1 tablespoon of the mayonnaise mixture on each triangle. Place the triangles on the baking sheet and bake until lightly golden, about 15 minutes. Serve warm.
Yield: 20 croutons