Tip: To dry and crumble 1 slice of bread, let the bread dry out overnight or bake at 300 degrees F until dry, about 8 minutes. Crumble with your hands or in a food processor.
To make ahead: Prepare through Step 4; cover and refrigerate for up to 1 day. To serve, continue with Step 5, baking for 20 to 25 minutes.
Equipment: Mini muffin tin with 24 (1 3/4-inch) cups. (If you don't have one, use a standard tin with 12 (2 1/2-inch) cups instead and bake tarts for 25 to 30 minutes.)