Preheat your oven to 350°F. Spread the bread cubes on a baking sheet and toast for 8–10 minutes until they are dry to the touch but not dark brown. This "stale" texture allows the bread to act like a sponge for the custard.

In a large bowl, whisk the eggs and brown sugar until pale. Gradually whisk in the milk, heavy cream, cinnamon, nutmeg, and vanilla paste.

Place the toasted bread cubes in a greased 9x9 baking dish. Pour the custard mixture over the bread. Use a spatula to gently press the bread down so every piece is submerged. Let it sit for 20 minutes before baking. This is the secret to a uniform, pudding-like center.

Place the dish in the oven and bake for 40–45 minutes. The pudding is done when the center is set but still has a slight jiggle, and the tops of the bread are golden and crisp.

While the pudding bakes, melt the butter in a small saucepan. Whisk in the sugar and heavy cream. Simmer for 5 minutes until thickened. Remove from heat and stir in the vanilla and salt.

Pour half of the warm sauce over the pudding immediately after it comes out of the oven. Serve the remaining sauce on the side.