Blackberry Dark Chocolate Blondies

Ingredients

• 1 3/4 cups (240g) blackberries, divided
• 2 tablespoons (25g) granulated sugar
• 1 teaspoon lemon juice
• 1 teaspoon cornstarch
• 3/4 cup (170g) unsalted butter, cubed
• 1 1/2 cups (192g) all purpose flour, sifted
• 1 teaspoon fine sea salt
• 1/2 teaspoon baking powder
• 1 1/4 cups (250g) packed brown sugar
• 1 large egg
• 1 large egg yolk
• 1 1/2 teaspoons pure vanilla extract
• 3 ounces (85g) dark chocolate, broken into bite size pieces