Oatmeal Raisin Bars

3/4 cup (1 1/2 sticks) unsalted butter, melted, plus more for pan
3/4 cup packed light-brown sugar
1/4 cup granulated sugar
1 large egg
1/2 teaspoon salt
1/2 teaspoon ground cinnamon
1 cup all-purpose flour (spooned and leveled)
2 cups old-fashioned rolled oats (not quick-cooking)
1 cup raisins
Directions
Preheat oven to 350 degrees. Butter an 8-inch square baking pan. Line bottom with parchment paper, leaving an overhang on two sides; butter paper.
In a large bowl, whisk together butter, sugars, egg, salt, and cinnamon until smooth. Add flour, oats, and raisins; fold in just until combined.
Spread batter in prepared pan, and bake until a toothpick inserted in center comes out with moist crumbs attached, 25 to 30 minutes. Cool completely in pan. Using paper overhang, lift cake onto a work surface; cut into 16 bars.