1 1/2 cups walnut halves
6 large eggs
1 1/2 cups heavy cream, half-and-half, or milk
2 tablespoons pure vanilla extract
1/2 teaspoon ground cinnamon
Pinch of ground nutmeg
Pinch of salt
6 ripe but firm bananas, peeled and cut into 1/4-inch rounds
1 1/2 cups packed dark-brown sugar
12 slices of bread, (1/2 inch thick), such as brioche or challah, preferably day old
8 tablespoons (1 stick) unsalted butter
4 tablespoons vegetable oil
Pure maple syrup, for serving (optional)