Preheat oven to 375°. Rub an 8-inch square baking dish with 1 tablespoon melted butter.
In a large bowl, combine oats, ¼ cup almonds, pie spice, and baking powder. In a medium bowl, whisk together milk, honey, egg, 2 tablespoons melted butter, and vanilla. Stir milk mixture into oat mixture. Sprinkle 1¼ cups blackberries in prepared pan. Top with oat mixture, remaining ½ cup blackberries and remaining ¼ cup almonds. Drizzle with remaining 1 tablespoon melted butter.
Bake until bubbly and set, 30 to 35 minutes. Let stand for 5 minutes. Serve with maple syrup.
Recipe by The Ribbon in My Journal - Phyllis Hoffman DePiano at https://www.theribboninmyjournal.com/baked-blackberry-almond-oatmeal/