Roll 1 lemon on the counter with pressure to release the juices. Zest it with a microplane, then juice it. You will need 1 tablespoon zest for the custard, plus 1 teaspoon for the topping. You will need 3 tablespoons juice total for the custard and glaze.
Prepare a 9x13 baking dish with non-stick cooking spray.
Cut 1 loaf brioche or challah bread into 1" cubes.
Spread half the bread cubes evenly in the prepared dish.
Scatter half of 1½ cups fresh raspberries and half of ¼ cup sliced almonds over the bread cubes.
Repeat with the remaining bread cubes, raspberries, and almonds.
In a bowl, whisk together 6 large eggs, 1¾ cups milk, ½ cup plain Greek yogurt, ¼ cup honey or maple syrup, 1 teaspoon vanilla extract, ½ teaspoon almond extract, pinch salt, 1 tablespoon of the lemon juice, and 1 tablespoon of the lemon zest.
Pour the egg mixture evenly over the bread, raspberries, and almonds in the pan.
Press down on the bread slightly so it can soak up more of the egg mixture.
Cover the baking dish and refrigerate overnight.
Store the remaining lemon juice and zest in covered containers in the refrigerator overnight.
Baking
In the morning, preheat the oven to 350ºF.
Mix together 2 tablespoons sugar and 1 teaspoon lemon zest.
Sprinkle the lemon sugar mixture and ¼ sliced almonds evenly over the casserole.
Bake uncovered at 350ºF for 40-45 minutes until puffed, golden, and set in the center.
Glaze
Make the glaze by combining ½ cup powdered sugar and 2 tablespoons of the reserved lemon juice. Drizzle evenly over the baked casserole.
Optional garnishes
Scatter ½ cup fresh raspberries tossed with sugar over baked casserole.
Dust with powdered sugar. If desired, serve topped with whipped cream and/or raspberry jam.
Notes
Nutrition data does not include optional garnishes.