Preheat your oven to 350°F (175°C) and position a rack in the middle. Line an 8x8-inch square metal baking pan with foil, dull side up, leaving a couple of inches of overhang on two sides. This will make it much easier to lift out the bars for slicing later.

In a medium bowl, combine 8 tablespoons unsalted butter at room temperature, 1/3 cup powdered sugar, and 1/2 teaspoon kosher salt. Using an electric handheld mixer, beat on low speed to mix, then increase to medium and continue beating until smooth and well combined, about 2-3 minutes. Scrape down the sides as needed. Beat in 1 1/2 teaspoons vanilla extract. Add 1 cup all-purpose flour and mix on low until a crumbly dough forms. Fold the dough with a spatula to make sure there are no dry spots. Scatter the dough across the bottom of the prepared pan, then press it evenly using the back of a measuring cup or a small glass (use parchment or plastic wrap if it sticks). Chill the crust in the fridge for 10 minutes, then prick all over with a fork.

Bake the chilled crust for 15-20 minutes, until the surface appears matte and the edges are starting to color. While still warm, gently press down on the crust with the back of a glass to compress it. Allow the crust to cool on a wire rack while you prepare the filling. Don't turn off the oven, you'll need it again soon.

To make the filling, place 5 1/3 tablespoons unsalted butter in a light-colored saucepan over medium-low heat. Once melted, increase the heat slightly and cook, stirring frequently, until the butter foams, turns clear gold, and starts to brown, about 5-7 minutes—watch carefully to prevent burning. Carefully pour in 1/2 cup maple syrup, reduce heat to low, and stir until the syrup thickens and darkens slightly, about 2 minutes. Remove from the heat and scrape the mixture into a large bowl. Let cool for 5-10 minutes. Then whisk in 1/2 cup packed brown sugar, 1/2 teaspoon kosher salt, 1 1/2 teaspoons vanilla extract, 2 tablespoons heavy cream, 2 teaspoons apple cider vinegar, 2 large eggs, and 1 tablespoon all-purpose flour until smooth. Fold in 1 1/4 cups toasted and roughly chopped pecan halves. I like to toast the pecans beforehand for even deeper flavor—it makes a big difference!

Pour the maple pecan filling over the baked and cooled crust. Bake for about 25 minutes, until the filling is browned and appears set with just a slight jiggle in the center. Remove from the oven and sprinkle flaky salt over the top while it's still hot. Let the bars cool completely at room temperature. For the cleanest slices, I find it best to refrigerate the bars before cutting.

Once the bars are fully cooled and chilled, use the foil overhang to lift them out of the pan. With a serrated knife, cut them into your desired size and shape. Serve the bars slightly chilled or at room temperature for the best texture. Store any leftovers in an airtight container for up to 5 days, or freeze for longer storage. Enjoy!