Step 1

Place 2 sticks unsalted butter in the bowl of a stand mixer (or large bowl if using an electric mixer). Let sit at room temperature until softened.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 350ºF. Lightly coat an 8 1/2 x 5-inch loaf pan with cooking spray, then lightly coat with all-purpose flour, tapping out the excess.

Step 3

Place 2 1/4 cups all-purpose flour, 1 1/2 teaspoons baking soda, and 1 teaspoon ground cinnamon in a medium bowl and whisk to combine. Peel and grate 3 medium carrots on the large holes of a box grater or in a food processor fitted with the shredding disc until you have 2 cups.

Step 4

Add 3/4 cup granulated sugar and 3/4 packed light brown sugar to the bowl of butter. Beat with the paddle attachment on medium speed until the sugar is incorporated and fluffy, about 3 minutes. Scrape down the sides of the bowl with a flexible spatula. Add 3 large eggs, 1 teaspoon vanilla extract, and 1/4 teaspoon kosher salt. Beat on medium speed until fluffy, about 4 minutes.

Step 5

Reduce the speed to medium low. Beat in the flour mixture in 3 additions until just combined, scraping down the bowl halfway through, about 2 minutes total. Add the carrots and fold in by hand with the flexible spatula.

Step 6

Transfer the mixture to the pan, spread into an even layer, and smooth the top. Pick up the pan and bang the bottom on the counter to fill out the pan.

Step 7

Bake until a tester inserted in the center comes out clean, about 1 hour and 25 minutes. Check after 45 minutes and tent loosely with aluminum foil if the top is browning too quickly. Place on a wire rack and let cool in the pan for 15 minutes. Remove the loaf from the pan to the wire rack and let cool completely, about 1 hour and 15 minutes more.