For the Bottom Layer:
Heat the oven to 425 degrees F. Grease a 9" x 13" pan. In a large bowl, combine the oats, flour, brown sugar, baking soda, and salt. Stir in the melted butter and vanilla until thoroughly combined. Press this mixture evenly into the bottom of the pan with your fingers. (I also use the bottom of a stainless steel measuring cup to help make the crust flat and even.)

For the Top Layer:
Place the flour, brown sugar, and butter or vegetable oil sticks in a small bowl and use a fork, pastry blender, or your fingers to combine until the mixture resembles large crumbs (some pea-sized clumps are okay). Set aside.

For the Middle Layer:
Place the blueberries in the bowl you mixed the Bottom Layer in and toss them with the almond extract. Pour them evenly over the Bottom Layer in the pan. Combine the sugar and flour and sprinkle it evenly over the blueberries. (Even when wet or frozen, the sugar/flour mixture wouldn't stick to my big fat blueberries when I tried tossing it with them. If yours will, just toss the sugar/flour mixture with the blueberries and then pour the whole mixture over the Bottom Layer in the pan.)

Sprinkle the Top Layer evenly over the blueberry mixture. Bake at 425 degrees F for 15 minutes, then lower the oven temperature to 350 degrees F and bake for another 20 to 25 minutes, until the top is golden, and the edges are starting to brown. Let cool in pan on a wire rack. Store in a cool place or refrigerate. Bars may also be frozen.

Just Peachy Blueberry Breakfast Bars:  Substitute 3 cups of small peach chunks (about 2 peaches, no need to peel them) and 2 cups of fresh or frozen blueberries for the 3-1/2 cups of blueberries. Toss the sugar and flour directly with the fruit before spreading it over the bottom layer. Bake at 425 degrees for 15 minutes, then lower the oven to 350 degrees and bake until topping looks "dry" but edges aren't too brown, about 30 to 40 minutes.