Preheat the oven to 375 degrees F (190 degrees C). In an 8 or 9-inch baking pan, mix together the Sliced Almonds (1/2 cup), the Ground Cinnamon (1 1/2 teaspoon), Baking Powder (1 teaspoon), Steel-Cut Oats (3/4 cup) and if using, and Fine Sea Salt (1/2 teaspoon). Place the Fresh Blueberries (3/4 cup) on top.
In a medium bowl, whisk together the Whole Milk (2 cup), Maple Syrup (1/4 cup), Large Egg (1), Unsalted Butter (3 tablespoon) and Vanilla Extract (2 teaspoon). Pour the milk mixture over the oat mixture, and shake the pan to distribute.
Transfer pan to the oven and bake for 55 to 60 minutes or until the top is golden and the oat mixture has set. Remove from the oven, and allow to cool for a few minutes before serving. If it seems like it's browning too quickly, turn down the oven slightly.