Crust

1. Preheat oven to 350 degrees farenheit. 
2. Prepare a 9x9 baking pan by spraying cooking spray or greasing with a bit of butter. I like to then lay a sheet of parchment paper in the pan. Slit the corners so they overlap and trim any excess. Having the parchment paper will allow you to remove bars from the pan easily. Otherwise, note you will need to cut directly in the pan (be aware if you are using a non-stick pan).
3. In a microwave safe bowl large enough for all your crust ingredients, cut your butter into slices and heat until just melted. Begin with 30 seconds and add 10 seconds at a time as needed.
   • 1 stick of butter, 113 grams (I actually like salted here but unsalted works fine too)
4. Add in your powdered sugar, flour, baking powder, lemon zest and salt. Combine with a fork to start then spatula until a dough forms. 
   • 1/2 cup powdered sugar, 50 grams
   • 1 cup + 2 Tablespoons flour (spooned and leveled), 140 grams
   • 1/2 teaspoon baking powder
   • zest of 1 lemon
5. Press your dough into your prepared pan until you have an even layer. You can use the bottom of a measuring cup to help you press evenly into place or simply work with your hands.
6. Prick the dough with a fork several times and bake for 20-25 minutes until golden brown. Remove and let cool slightly.

Crumble Topping

1. In the same bowl you made your crust, prepare your crumble topping.
2. Cut your butter into slice and melt for about 30 seconds. 
   • 5 Tablespoons butter - melted, (salted or unsalted is fine), 70 grams
3. Add your flour, oats, brown sugar, butter, cinnamon, cardamom and salt. Work together with fork or spatula until small crumbles form. Set aside.
   • 1/2 cup flour, 60 grams
   • 1/2 cup whole old-fashioned oats, 45 grams
   • 1/3 cup brown sugar, 67 grams
   • 1 teaspoon ground cinnamon
   • 1/2 teaspoon ground cardamom
   • pinch of salt (if using unsalted butter)

Blueberry Filling

1. In a medium sized pot, add your washed blueberries and remaining filling ingredients.
   •  
   • 18 ounces fresh or frozen blueberries (about 3.5 cups) - 510 grams
   • 1/2 cup brown sugar, 100 grams
   • 2 Tablespoons corn starch
   • zest of 1 lemon
   • juice of 1 lemon
   • 1 teaspoon vanilla extract
   • 1 teaspoon ground cinnamon
   • 1 teaspoon ground cardamom
   • 1 teaspoon black pepper*
2. Place your pot of blueberry mixture on the stove and heat on medium-high for 10-12 minutes. Stir frequently to ensure the mixture doesn't burn. Cook until the liquid begins to thicken then remove from heat.
3. Pour the blueberry mixture onto the prepared crust and top with prepared crumble topping.
4. Place in preheated 350 degree Fahrenheit oven to bake for another 45-50 minutes until blueberry filling is bubbling and top is golden brown.
5. ALLOW TO FULLY COOL before cutting or removing from pan. Cutting or removing while hot will cause the blueberry filling to spill over. 
6. Enjoy as is or with a scoop or ice cream or yogurt!