Grease a muffin tin with butter or oil. Divide the bread and berries evenly among the 12 muffin cups, pressing them in to fit if needed.
Combine the eggs, milk, half-and-half, banana, vanilla, and cinnamon in a blender and blend until smooth. Pour the custard mixture into the muffin cups, using a spoon to press down and submerge the bread.
Preheat the oven to 325ºF.
While the oven is preheating, use the spoon to press down on the bread periodically to make sure the custard soaks into it. Once preheated, place the muffin tin in the oven and bake the cups for about 35 minutes, or until the custard is set and the edges of the cups are golden brown.
Allow the cups to cool for 5-10 minutes, then run a butterknife along the edges of each cup and carefully remove.
To freeze, transfer the cups to a parchment-lined baking sheet and place in the freezer until frozen through. Pop the frozen French toast cups in a freezer bag; to reheat, microwave until warm or bake in the oven at 350ºF for 10-15 minutes.