• Preheat the oven to 350°F. Line an 8x8 metal baking pan with parchment paper. Set aside.

Prep the fruit filling.

• In a medium pan, combine berries, sugar, cornstarch, lemon juice, and salt. Stir to coat the berries.
  12 ounces fresh or frozen berries, ¼ cup granulated sugar, 1 tablespoon cornstarch, 2 teaspoons lemon juice, 1 pinch fine sea salt
• Cook the filling on the stove on medium-low heat until the berries release their juices, about 10 minutes. Stir the mixture frequently while cooking.
• Turn the heat up to medium and continue to cook, stirring frequently, until the filling thickens and begins to bubble, about 5 more minutes. Let the filling cook while bubbling for 1 minute.
• Remove the pan from the heat and let the filling cool slightly while you make the crumble dough.

Make the crumble dough

• In a large bowl, add oats, flour, brown sugar, baking powder, and salt. Whisk to combine.
  1 ½ cups old-fashioned oats, 1 ½ cups all-purpose flour, 1 cup light brown sugar, ½ teaspoon baking powder, ½ teaspoon fine sea salt
• Add melted butter and toss gently with a fork until a dough forms.
  ¾ cup unsalted butter

Assemble and bake the bars.

• Add ⅔ of the crumble dough to the prepared pan. Use your hands to gently press the dough into the pan to form a crust that reaches the edges of the pan.
• Parbake the crust in the oven for 10 minutes or until golden. Remove from the oven and let sit for 2 minutes.
• Carefully spread the berry filling over the crust.
• Use your fingers to crumble the remaining dough over the berry filling.
• Return the pan to the oven and bake for another 20-25 minutes, or until the filling is bubbling and the crumbles on top are golden.
• Let cool before slicing and serving.