1-Preheat your oven to 350°F and line a 9×13 baking pan with parchment paper or foil sprayed with non-stick spray.

2-In a mixer bowl, beat the softened butter and granulated sugar until light and fluffy, about 3 minutes.

3-Add the vanilla and maple extracts, then mix in the eggs one at a time until just combined.

4-In a separate bowl, whisk together the flour, baking powder, and salt.

5-Add the dry ingredients and roughly chopped hazelnuts to the wet mixture, mixing on low until just moistened (the dough will be very thick).

6-Transfer the dough to the prepared pan and use buttered hands or a spatula to spread it evenly to the edges.

7-Bake on the center rack for 20-22 minutes, until the edges are set and slightly browned but the center still looks a bit underdone.

8-Avoid over-baking to keep the bars moist, as they will continue to set while cooling.

9-Allow the bars to cool completely on a rack before frosting.

10-Melt the butter in a saucepan over medium heat, swirling occasionally until golden brown solids form and it smells nutty.

11-Remove from heat, scrape into a bowl, and let cool to a solid at room temperature.

12-Beat the cooled browned butter for 1 minute until smooth.

13-Add the powdered sugar, salt, vanilla extract, and maple extract.

14-Beat for several minutes until light and fluffy.

15-Fold in the finely chopped hazelnuts, reserving some for topping.

16-Lift the cooled bars from the pan using the parchment paper, peel off the paper, and place on a cutting board.

17-Spread the frosting evenly over the bars, sprinkle with the reserved hazelnuts, and cut into bars.