Step 1

Combine blackberries, blackberry preserves, white sugar, cornstarch, and 1/8 teaspoon kosher salt in a small saucepan.

Step 2

Heat on medium-high heat, stirring constantly, until the mixture comes to a boil. Reduce heat to medium, and continue stirring, occasionally, 7 to 10 minutes, making sure the mixture doesn't stick to the bottom of the pan.

Step 3

When the mixture has thickened, remove from the heat and allow to cool.

Step 4

Preheat the oven to 350 degrees F (175 degrees C) and line an 8x 8-inch baking pan with a large piece of parchment paper, covering the bottom and coming up on 2 sides, to make a sling. Spray parchment paper and exposed sides of the pan with cooking spray.

Step 5

Combine oats, flour, light brown sugar, sliced almonds, cinnamon, soda, and salt in a bowl; stir until well mixed. Drizzle in melted butter, tossing and stirring the crumble ingredients until the flour and oats are incorporated.

Step 6

Spread out 2 cups of the crumble mixture onto the prepared pan, using finger tips or the bottom of a measuring cup to firmly flatten and smooth.

Step 7

Pre-bake in the preheated oven about 10 minutes. Remove from oven and allow to cool for 5 minutes.

Step 8

Pour filling over the crust, and sprinkle on remaining crumble mixture evenly over the top. Return the pan to the oven and bake until the top is lightly browned and the filling is bubbly, about 40 minutes.

Step 9

Cool completely in the pan, 1 to 2 hours.

Step 10

When the bars are cool, use the parchment to lift the them out of the pan. Cut into 9 servings, and serve at room temperature. Refrigerate any leftovers.