Prepare a 9-inch by 9-inch baking pan by greasing the pan with oil or butter, then lining it with parchment paper.

Preheat oven to 350ºF

In a large mixing bowl, add the melted butter, cookie butter, and brown sugar. Mix until light and fluffy.

Then add in the eggs, one at a time, until fully incorporated.

Next, sift in the flour, baking powder, and salt.

Mix into the batter just until incorporated, without overmixing.

Pour the batter into the prepared baking pan.

Bake for 25-30 minutes, until a toothpick poked into blondie comes out clean.

Cool in pan for 15-30 minutes, then remove onto a wire rack to cool completely.