Step 1

Preheat oven to 350 degrees F. Line an 8-inch-square baking pan with parchment paper, allowing it to overhang the edges. Coat the paper and pan sides with cooking spray.

Step 2

Whisk brown sugar and oil in a large bowl until combined. Add eggs and vanilla and whisk until combined. Combine rye flour, all-purpose flour, baking powder and salt in a medium bowl. Add the dry ingredients to the wet ingredients, stirring until just combined. Fold in 1/2 cup chocolate. Scrape the mixture into the prepared pan and sprinkle with the remaining 1/4 cup chocolate and flaky salt.

Step 3

Bake until a toothpick inserted in the center comes out clean, 25 to 30 minutes. Let cool in the pan on a wire rack for 1 hour before cutting into squares.