1. Begin by combining the mayonnaise and Dijon mustard in a small bowl. Mix until smooth.
2. For the sandwich, spread one of the slices of bread with the Dijon and mayonnaise mixture and top with 2 slices of bacon.
3. On the other slice of bread, place 2 slices of bacon, followed by 2 slices of Castello® Saga brie.
4. Fold the sandwich together and butter the outer sides of the bread with butter. Repeat for remaining sandwiches.
5. Heat a Panini grill or frying pan over medium heat. Grill each sandwich until golden brown and the Saga Blue Brie has melted, about 3-4 minutes a side.
6. Remove and open the sandwich and add a few slices of avocado and the butter lettuce. Close the sandwich and serve immediately while still warm.