Whisk together the milk, vanilla extract, almond extract, eggs, brown sugar, cinnamon, nutmeg, and salt in a large low-line bowl (easy for dipping a croissant).
Make sure the croissants are cut in half. Dip croissant halves into egg mixture until fully coated.
Lay the croissants into a prepared 9x13 dish, overlapping them until they are squeezed together. Pour the remaining egg mixture over the croissants, gently pressing down with your hands to absorb.
In between the croissants, tuck about 3/4 cup (total) of strawberries and blueberries in between the layers. Sprinkle the remaining berries over the top of the casserole. Cover the dish with plastic wrap and refrigerate for at least 2 and or up to overnight.
Preheat the oven to 350 degrees F. Remove the casserole from the refrigerator 30 minutes before baking and let it stand at room temperature.
Cover with foil and bake for 30 minutes.
Remove the foil and bake for an additional 15-20 minutes until golden brown.
Allow to sit for 10 minutes (with foil back on to keep hot), before serving.
Dust with powdered sugar and serve with a dab of whipped cream, and a drizzle of maple syrup!