Step 1: Prepare the Bread: Arrange the bread cubes in a single layer on a baking sheet and let them sit out for a few hours, or overnight, to become slightly stale. Alternatively, you can toast them lightly in a 300°F (150°C) oven for 10-15 minutes.
Step 2: Whisk the Custard: In a large bowl, whisk together the eggs, heavy cream, whole milk, 1 cup packed light brown sugar, granulated sugar, bourbon (if using), 2 tablespoons melted unsalted butter, vanilla extract, cinnamon, nutmeg, and salt until well combined and smooth.
Step 3: Combine with Bread: Place the stale bread cubes in a large 9x13 inch baking dish. Pour the custard mixture evenly over the bread, gently pressing down to ensure all the bread is submerged and coated. Let it sit at room temperature for at least 30 minutes, or up to 2 hours, allowing the bread to soak up the custard. For best results, cover and refrigerate overnight.
Step 4: Prepare Pecan Topping: In a medium bowl, combine the chopped pecans, 1/2 cup packed light brown sugar, 1/4 cup melted unsalted butter, 2 tablespoons heavy cream, 1 teaspoon vanilla extract, and a pinch of salt. Mix until the pecans are evenly coated.
Step 5: Bake the Bread Pudding: Preheat your oven to 350°F (175°C). If the bread pudding has been refrigerated, let it sit at room temperature for about 20-30 minutes before baking. Sprinkle the pecan topping evenly over the soaked bread pudding mixture.
Step 6: Bake until Golden: Bake for 45-55 minutes, or until the custard is set (a knife inserted into the center comes out mostly clean) and the topping is golden brown and bubbly. If the topping starts to brown too quickly, you can loosely tent it with aluminum foil.
Step 7: Cool and Serve: Remove from the oven and let the bread pudding cool for at least 15-20 minutes before serving. This allows the custard to fully set. Serve warm with vanilla ice cream, whipped cream, or a drizzle of caramel sauce.