Start by preheating your oven to 350°F (175°C).
Slice the apple into eight even pieces and set aside. In a small bowl, combine the brown sugar and 1 teaspoon of ground cinnamon. Mix thoroughly.
Open the can of crescent rolls and unroll the dough. Lay the triangles in your greased 9x13-inch baking dish, covering the bottom.
Evenly distribute the apple slices over the crescent rolls. Sprinkle the cinnamon-sugar mixture over the apples.
In a mixing bowl, whisk together the granulated sugar, heavy cream, almond extract, and egg until combined.
Carefully pour the custard mixture over the crescent rolls and apple slices, covering everything evenly.
Sprinkle the sliced almonds on top of the casserole.
Sprinkle ½ teaspoon of ground cinnamon over the top.
Place the casserole in the preheated oven and bake for about 30-35 minutes, or until golden brown and set.
Let the casserole cool for a few minutes before slicing. Serve warm and enjoy!