For the Bread Pudding:

1. Prepare the bread. If the bread is fresh, spread the cubes on a baking sheet and dry in a 300°F (150°C) oven for 10–15 minutes until the exterior is dry but not toasted. If using genuinely stale (1–2 day old) bread, proceed without drying. The cubes should feel dry to the touch.
2. Make the custard. In a large bowl, whisk together the heavy cream, whole milk, eggs, egg yolks, granulated sugar, brown sugar, vanilla extract (or vanilla bean seeds and pod), nutmeg, salt, and melted butter until smooth and fully combined.
3. Soak the bread. Add the bread cubes to the custard bowl. Gently press all the cubes down to ensure every surface is in contact with the custard. Let soak for a minimum of 30 minutes at room temperature, pressing down occasionally. For the overnight method — the recommended approach — cover the bowl and refrigerate for 8–12 hours.
4. Prepare the slow cooker. Generously grease the slow cooker insert with butter, covering the bottom and sides completely. Remove the vanilla bean pod from the custard if using. Transfer the soaked bread mixture to the slow cooker insert, spreading evenly. Pour any remaining custard from the bowl over the top.
5. Set up the slow cooker. Lay 2 full sheets of paper towels flat across the top of the slow cooker opening. Place the lid on top, securing the paper towels between the lid and the rim to absorb condensation.
6. Cook. For a softer, more custardy result: cook on LOW for 3.5 to 4.5 hours. For a firmer, more structured pudding: cook on HIGH for 2 to 2.5 hours. The pudding is done when the custard is fully set — a knife inserted in the center comes out clean rather than wet — and the edges are golden and beginning to pull away from the sides.
7. Rest. Turn off the slow cooker. Remove the lid and allow the bread pudding to rest for 15 minutes before serving. This allows the custard to finish setting and makes it easier to scoop or slice.

For the Vanilla Sauce:

8. Prepare the base. In a medium bowl, whisk together the egg yolks and sugar until pale and slightly thickened, about 1–2 minutes.
9. Heat the cream. Pour the heavy cream into a small saucepan and heat over medium heat until just simmering — small bubbles at the edges, not a full boil.
10. Temper the eggs. Very slowly pour about ¼ cup of the hot cream into the egg yolk mixture, whisking constantly and quickly. This gradually raises the temperature of the eggs without scrambling them. Then slowly pour the tempered egg mixture back into the saucepan with the remaining hot cream, whisking constantly.
11. Cook the sauce. Return the saucepan to medium-low heat. Cook, stirring constantly with a wooden spoon or heat-proof spatula, until the sauce thickens enough to coat the back of the spoon and a finger drawn through it leaves a clean line, about 4–6 minutes. Do not let it boil.
12. Finish the sauce. Remove from heat immediately. Stir in the butter until melted and glossy. Stir in the vanilla extract and salt. Strain through a fine mesh sieve into a warm jug for the smoothest result.
13. Serve. Scoop or slice the warm bread pudding into bowls or onto plates. Pour the warm vanilla sauce generously over each serving. Dust with a little ground cinnamon and powdered sugar if desired. Serve immediately.