FOR THE BLACKBERRY FILLING

1. Place the blackberries, sugar, water, lemon zest and corn starch in a medium pan and bring to a simmer.
2. Mash the berries with a spatula as they cook to help them break down.
3. Stir frequently and continue to cook until the mixture has thickened in texture and coats the back of a wooden spoon/spatula.
4. Remove from heat, stir in vanilla and allow to cool for about 10 minutes.

FOR THE OAT CRUMBLE CRUST

1. Preheat oven to 350 degrees and line an 8×8 glass pan with parchment paper.
2. In a standing mixer fitted with the paddle attachment (or using a handheld mixer), cream together butter and sugars for 2 minutes on medium high heat, until lightened in color and fluffy.
3. Reduce mixer speed and add egg and vanilla. Scrape down sides of bowl if needed.
4. In a separate bowl, whisk together flour, oats, baking soda, cinnamon, nutmeg and salt.
5. Keeping mixer on low speed, mix dry ingredients into wet ingredients.
6. Place half of batter into prepared pan and spread to edges. Pre-bake bottom crust for about 15 minutes until it’s set and let cool for a few minutes.
7. Spoon blackberry filling over pre-baked crust. Crumble the remaining dough over the top.
8. Spoon blackberry filling over cooled crust and crumble reserved dough over filling.
9. Bake bars for another 30 minutes, or until topping is golden brown and filling is bubbling.
10. Cool completely before lifting parchment out of the pan and cutting. To make cutting even easier, refrigerate the cooled bars before cutting.
11. Store bars in an airtight container in the refrigerator.