Recipe Notes From the New York Times, originally adapted from Stir, Bake by Charlotte Druckman.
Makes about 2 dozen bars.
1 cup unsalted butter, cold, plus more for buttering the pan
½ teaspoon salt
1 teaspoon vanilla extract
1 cup soft-packed dark brown sugar
2 cups all-purpose flour
1 cup slivered or sliced almonds, toasted, or 6 ounces chocolate chips or chunks
Preheat oven to 350°F. Position a rack in the center, and place a 10-inch cast-iron skillet on it.
In the bowl of a stand mixer fitted with a paddle attachment, beat the butter on low speed for about a minute, until softened. Scrape down the bowl and the paddle.
With the mixer running at low speed, add the salt and vanilla. Add the brown sugar, then turn the speed up to medium and beat until mixture is fluffy and the color of peanut butter, 1 to 2 minutes. Scrape down the bowl again.
With the mixer running at low speed, shake in flour, beating just until dough holds together. Mix in nuts or chocolate just until combined.
Remove the hot skillet from the oven and place a small lump of butter in it. As butter melts, brush it onto the bottom and sides of the pan until evenly coated.
Dump the dough into skillet and press it out evenly to fill the skillet. You can use your fingers (being careful to avoid touching the hot pan!), a potato masher, or the bottom of a measuring cup. Press dough down firmly to make a compact, even layer.
Return the skillet to the oven and bake for 30 to 40 minutes, until the top is golden brown.
Remove from the oven and let cool in the pan. If necessary, run a butter knife around the sides of the pan to loosen. Cut bars into squares or diamonds.
Let the bars cool completely before removing from the pan. Use a small offset spatula or butter knife to transfer them to paper towels to blot the buttery bottoms.
Serve immediately or store in an airtight container, where they’ll keep well for up to 1 week.