Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper, lay bacon in a single layer, and bake for 15–18 minutes until crisp. Let it cool on paper towels, then crumble and set some aside for garnish.
In a bowl, beat softened cream cheese until smooth. Add powdered sugar, maple syrup, and bourbon if using. Mix until creamy, then fold in crumbled bacon. The filling should be thick and spreadable.
Pair up the brioche slices. Spread 2–3 tablespoons of filling on one slice, top with the other, and press gently to form sandwiches.
In a large bowl, whisk together eggs, milk, cream, bourbon, maple syrup, vanilla, cinnamon, nutmeg, and salt. Pour into a shallow dish for dipping.
Heat a skillet or griddle over medium heat and melt 1 tablespoon of butter. Dip each sandwich into the custard, soaking each side for 20–30 seconds. Cook for 3–4 minutes per side until golden and crisp. Repeat with remaining sandwiches, adding more butter as needed.
Cut sandwiches diagonally and serve with a drizzle of maple syrup, a dusting of powdered sugar, and the reserved crumbled bacon. Add berries or whipped cream if you like.