Preheat the oven to 350°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. Set aside.

In a large bowl, whisk brown sugar and oil until combined.

Add eggs and vanilla and whisk until combined.

In a medium bowl, stir together the rye flour, all-purpose flour, baking powder and 1/2 teaspoon flaky salt.

Add the dry ingredients to the wet ingredients, stirring until just combined.

Fold in 3/4 cup chocolate chips.

Scrape the mixture into the prepared pan and sprinkle with the remaining 1/4 cup chocolate chips and 1/4 teaspoon flaky salt.

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.