Preheat oven to 350°F. Spread the pecans evenly on a rimmed baking sheet and toast for 7 to 10 minutes, tossing halfway through, until lightly browned and fragrant. Remove from the oven and let cool.
Bourbon Sauce
Melt butter in a small saucepan over medium heat. Whisk in brown sugar, nutmeg, cinnamon, and vanilla. Once combined, add the heavy cream and simmer until slightly reduced. Add the bourbon and continue cooking until the sauce reaches the desired consistency.
Croissant Bread Pudding and Crust
Preheat oven to 400°F. Tear the croissants into smaller pieces and place in a large bowl.
In a separate bowl, whisk together the eggs and brown sugar until smooth. Add cinnamon, nutmeg, and vanilla, then slowly whisk in the half and half.
Pour the custard over the croissants and gently toss until the liquid is absorbed. Transfer to a parchment-lined 9 × 13-inch baking dish and press into an even layer.
Mix the softened butter and brown sugar until sandy in texture. Roughly break up the toasted pecans and stir them into the butter mixture. Spread evenly over the croissants. Arrange the sliced peaches over the top.
Bake for about 45 to 60 minutes, or until the custard is set and the top is golden and caramelized.
To Serve
Serve warm with bourbon sauce, whipped cream, or vanilla ice cream.
