Preheat the oven to 350° Arrange rack in the middle of the oven. Line an 8x8-inch baking dish with parchment paper, leaving a 2-inch overhang on two opposite sides.
Place the butter, maple syrup, eggs, peanut butter and vanilla in a large bowl. Beat with hand mixer until well-combined, about 1 minute. Add the flour, baking powder, and salt. Use a large spatula to mix until just combined.
Transfer batter to the prepared pan and smooth into an even layer. Bake until the edges are browned and pulling away from the pan or a tester inserted in the center comes out clean. 25 to 30 minutes.
Cool blondies in the pan on a wire rack for 10 minutes. Grasp the excess parchment paper and lift the blondie slab out of the pan and onto a cutting board. Cut into 16 squares.