Vanilla Buttermilk and Raspberry Baked French Toast

Name: Vanilla Buttermilk and Raspberry Baked French Toast
Ingredients: 6 eggs, lightly beaten; 1 1/4 cups (10 fl. oz./310 ml) buttermilk; 1 cup (8 fl. oz./250 ml) whole milk; 3 Tbs. firmly packed light brown sugar; 2 Tbs. vanilla bean paste; 1 tsp. ground cinnamon; 1/4 tsp. kosher salt; 1 loaf challah bread, about 1 lb. (500 g), cut into slices 1 inch (2.5 cm) thick; 2 Tbs. cold unsalted butter, cut into 1/4-inch (6-mm) cubes, plus butter for greasing; 1/4 cup (2 1/2 oz./75 g) raspberry preserves; 1 pint (8 oz./250 g) mixed berries, such as raspberries, strawberries and blackberries; Maple syrup for serving