Preheat the oven to 350 degrees F.
Making the baked croissant French toast casserole: In a large bowl beat the milk, cream, sugar and eggs until well blended. Add the sea salt, cinnamon and nutmeg. Add the dried blueberries and croissants, and let it all sit for 30 minutes, stirring occasionally to help the croissants absorb the liquid.
Grease an 8-inch square, high-sided casserole dish with the butter. Pour in the croissant/egg/milk mixture. Bake in the center of the oven until no liquid rises when the center of casserole is pressed, 45 to 55 minutes.
Making the bacon and bourbon infused maple syrup: Mince the bacon and fry until very crisp, about 8 minutes. Drain all the fat. Mix the maple syrup and bourbon and add the bacon. Refrigerate.
Making the caramelized shallot hazelnut butter: Saute the shallots in the unsalted butter over medium heat until caramelized, about 10 minutes. Remove from the heat and allow to cool slightly. Add the shallots to a medium bowl. Add the softened salted butter, hazelnuts and vanilla extract to the bowl, and stir with a wooden spoon until well blended. Place a large piece of plastic wrap on the counter and add the shallot hazelnut butter. Roll the butter in the plastic wrap to form a cylinder. Chill until firm.
Serve the baked croissant French toast casserole warm, adding a slice of caramelized shallot hazelnut butter to each portion. Drizzle generously with bacon and bourbon infused maple syrup.