For the Mayo Sauce
1. Mix the two ingredients well.
2. Store well in the fridge up to two days.
For the Sandwich:
1. Preheat oven to 425.
2. Butterfly sandwich baguette rolls.
3. Generously smear a few tablespoons of mustard mayo sauce on both sides of the bread.
4. Add ¼ of the ham to each roll and lay 2 slices of thick-cut brie on top of the meat.
5. Place in a cast iron skillet or on a cookie sheet in oven about 7 minutes or until bread and mayo sauce is golden and bubbly and cheese is soft and melted but still holding its shape. Remove from oven, place at least 4 thin slices of Granny Smith apple onto the sandwiches