Step 1

Preheat the oven to 375°. Line a 15-by-17-inch rimmed baking sheet with parchment paper. In a standing mixer fitted with the paddle attachment, beat the butter with the sugar at medium speed until light and fluffy, about 2 minutes. At low speed, beat in the flour and salt until a soft dough forms.

Step 2

Press the dough over the bottom of the prepared pan creating an even layer. Bake in the center of the oven for about 20 minutes, until the crust is golden and set. Let cool on a rack.

Step 3

In an extra large skillet, melt 6 tablespoons of the butter with 1/2 cup of the light brown sugar. Add the apples to the skillet and cook over high heat, stirring occasionally, until softened, about 10 minutes. Stir the cinnamon and nutmeg.

Step 4

Cook until the apples are caramelized and very tender and the liquid is evaporated, about 10 minutes longer; scrape up any bits stuck to the bottom of the skillet and if necessary, add up to 1/2 cup of water to prevent scorching. Let cool. (I did not need to add any water to my skillet.)

Step 5

In a large bowl, mix the oats with the flour, light brown sugar, cinnamon, baking soda and salt. Using a pastry blender to cut in the butter until the mixture resembles coarse meal. Stir in the pecans and press the mixture into clumps.

Step 6

Spread the apple filling over the crust. Scatter the crumbs on top, pressing them lightly into an even layer. Bake in the center of the oven for 1 hour, until the topping is golden; rotate the pan halfway through baking. Let cool completely on a rack before cutting into 2-inch bars.