Step 1

Cut 2 sticks unsalted butter into 1/2-inch cubes. Melt in a small, tall-sided saucepan over medium-high heat. Continue cooking, stirring constantly while scraping the bottom of the pot with a rubber spatula to release any browned bits, until the butter is light brown, smells nutty, and no longer foamy, about 6 to 12 minutes. Immediately scrape into a large heatproof bowl.

Step 2

Add 3 cups apple cider or unfiltered apple juice to the now-empty pan. (Be careful; the apple cider will sizzle when added to the hot saucepan.) Cook over high heat, stirring occasionally, until the cider has reduced to 1/2 cup, 30 to 40 minutes. (The easiest way to see if your cider has reduced enough is to carefully pour it into a liquid measuring cup and check if it’s at the 1/2-cup mark. If you accidentally overreduced it, just add enough water to bring it up to 1/2 cup.) Immediately pour the reduced apple cider into the bowl of melted butter and let cool at room temperature for 30 minutes.

Step 3

Meanwhile, arrange a rack in the middle of the oven and heat the oven to 350°F. Coat a 9x13-inch baking pan with cooking spray and line with parchment paper, leaving a 2-inch overhang on two opposite sides like a sling. Place 2 tablespoons of the granulated sugar and 1 teaspoon of the ground cinnamon in a small bowl and stir to combine.

Step 4

Place 3 cups all-purpose flour, the remaining 1 teaspoon ground cinnamon, 1 teaspoon kosher salt, 3/4 teaspoon baking soda, 1/4 teaspoon ground nutmeg, and 1/4 teaspoon ground allspice in a medium bowl and whisk to combine.

Step 5

When the butter and cider are ready, add 2 cups packed light brown sugar and the remaining 1/4 cup granulated sugar to it. Whisk until smooth and the sugar is mostly dissolved. Add 2 large eggs and 1 tablespoon vanilla extract and whisk until no streaks of egg remain. Add the flour mixture and stir with a rubber spatula until no pockets of dry flour remain and a smooth batter forms.

Step 6

Transfer the batter into the prepared baking pan and smooth into an even layer with an offset spatula or the back of a spoon. Sprinkle evenly with the cinnamon-sugar mixture and press it in slightly so it sticks.

Step 7

Bake until the top is browned and a toothpick inserted into the center comes out with only a few moist crumbs attached, 35 to 41 minutes. Let cool for at least 1 hour in the pan before slicing.