1. The night before serving, generously butter a 9×13-inch baking dish.

2. Arrange brioche slices in the dish, overlapping them slightly in a shingled pattern. They should fit snugly but not be crammed.

3. In a large bowl, whisk together eggs, whole milk, heavy cream, granulated sugar, vanilla extract, cinnamon, nutmeg, and salt for 2-3 minutes until completely smooth and sugar is dissolved.

4. Pour custard mixture evenly over bread slices, making sure every piece is covered. Use a spatula to press down gently on bread to encourage absorption.

5. Cover dish tightly with plastic wrap or aluminum foil and refrigerate overnight (at least 8 hours, up to 24 hours). Press down on bread once or twice during soaking if possible.

6. The next morning, remove from refrigerator and let sit at room temperature for 30 minutes. Preheat oven to 350°F (175°C).

7. Remove cover and press down on bread one final time. Bread should be completely saturated and custardy.

8. Bake on middle oven rack for 45-55 minutes, until custard is set and top is golden brown. Insert a knife in center—it should come out mostly clean. If top browns too quickly, tent with foil.

9. Remove from oven when done and increase oven temperature to broil (or prepare your kitchen torch).

10. In a small bowl, mix together brown sugar, granulated sugar, and melted butter until it forms a thick paste.

11. Spread sugar mixture evenly over top of baked French toast, covering entire surface with a ¼-inch thick layer.

12. Place under broiler for 2-4 minutes, watching constantly, until sugar melts, bubbles, and caramelizes to deep golden brown. Alternatively, use kitchen torch to caramelize sugar in sections.

13. Remove immediately when sugar reaches deep amber color. Let cool for 2-3 minutes until sugar hardens into a crackling crust.

14. Let rest for 5 minutes, then cut into squares and serve immediately with fresh berries, maple syrup, and powdered sugar.