Averie Cooks

-1 Preheat oven to 350F. Line an 8-inch square pan with aluminum foil and spray with cooking spray; set aside. Lining the pan will really help with cleanup and is recommended.
-1 Crust and Crumble Topping – In a large, microwave-safe bowl melt the butter, about 1 minute on high power.
-1 Add the sugars and whisk to combine.
-1 And the flour, optional salt, and stir to combine. Mixture will be very dry and sandy with some larger, well-formed crumble pieces.
-1 Set a heaping 3/4 cup crumble mixture aside.
-1 Transfer remaining mixture to prepared pan, and using a spatula or your fingers, hard-pack the mixture to create an even, smooth, flat crust; set aside.
-1 Berry Layer – In a separate medium bowl, add all filling ingredients and toss to combine.
-1 Evenly distribute berry mixture over the crust, smoothing it lightly with a spatula.
-1 Evenly sprinkle the reserved heaping 3/4 cup crust mixture. Before sprinkling, I squeeze the mixture in my palm to encourage bigger crumble pieces to form.
-1 Evenly sprinkle the walnuts.
-1 Bake for about 60 to 75 minutes (place pan on a cookie sheet for insurance against overflow if your pan is quite full), or until edges are bubbling quite vigorously and there’s some bubbling in the center. Crumble topping should appear set and very pale golden.
-1 Place pan on a wire rack and allow bars to cool for at least 2 hours (overnight is even better) before slicing and serving. After cooling overnight, I placed pan in the fridge 2 hours before slicing to ensure clean, neat cuts. If you try to slice bars before they’ve cooled completely, they’ll be extremely messy and could fall apart.