Preheat oven to 350°F (175°C). Lightly grease an 8x8 baking dish.
Make the filling: In a bowl, combine blackberries, maple syrup, lemon juice, arrowroot, and vanilla. Pour into the baking dish.
Make the topping: In a separate bowl, whisk together almond flour, coconut sugar, salt, and baking powder. Add melted butter, egg, and vanilla. Stir until a soft dough forms.
Assemble: Drop spoonfuls of the topping over the berries.
Bake for 30–35 minutes, until the top is golden brown and the berries are bubbling.
Let cool slightly before serving. Enjoy warm with a scoop of vanilla ice cream!