Preheat oven to 350°F (175°C). Grease an 8-inch square baking pan.
Whisk together the flour, baking powder, and salt. Set aside.
Using an electric mixer on medium speed, beat the butter and brown sugar until smooth. Add the eggs, one at a time, mixing until combined after each addition. Mix in the vanilla.
Reduce mixer speed to low and gradually add the flour mixture, mixing until combined. Stir in the cashews.
Spread the batter evenly in the prepared pan. Bake 35-40 minutes, or until a toothpick inserted in the center comes out with moist crumbs. Cool completely before cutting into bars.
Notes
*If using salted cashews, you may want to reduce salt to 1/2 teaspoon.