For best results, use slightly stale bread. This allows it to absorb the custard without becoming mushy. Feel free to substitute pecans or almonds for the walnuts in the crumb topping. If you prefer a richer flavor, use whole milk or half-and-half instead of milk. The bread pudding can be assembled ahead of time and refrigerated for up to 24 hours before baking. Add about 10-15 minutes to the baking time if baking from cold. Test for doneness by inserting a knife into the center; it should come out mostly clean.