Preheat the oven to 350°F (180°C). Spread the croissants on a large tray in a single layer and dry out in the oven for 10-15 minutes, this is especially important if you are using fresh croissants.
Grease an oven-safe deep ceramic dish, 8x11-inch (20x28cm), with a little butter.
Grill or panfry the bacon until crisp. Drain on kitchen towels and then cut into small pieces.
Put the eggs, milk, cream, mustard, salt, and garlic granules in a bowl and lightly whisk together to combine. Season generously with freshly ground pepper.
Stir in the grated cheese, reserving a small handful.
Line your dish with the croissant slices or cubes, packing them in so that they fill the dish edge-to-edge.
Pour half the egg mixture over them and scatter with half the bacon.
Add a second layer of croissant cubes or slices and pour the remaining egg mixture over them. Scatter with remaining bacon.
Cover the dish with cling film (plastic wrap) and press down with your hands so that the croissants are submerged in the custard. Place a weighted plate over them and keep in the fridge for 30 mins-1 hour.
When you are ready to bake, preheat the oven to 350°F (180°C) and remove the dish from the fridge to come to room temperature.
Bake for 25 minutes and then sprinkle with the reserved Comté cheese. Continue to cook for a further 10-15 minutes until golden.