- 8 tablespoons (1 stick) unsalted butter, at room temperature, plus more for the pan
- 2 cups old-fashioned rolled oats (not quick-cooking)
- 1/2 cup all-purpose flour, spooned and leveled
- 1/2 teaspoon baking soda
- 1/2 teaspoon ground cinnamon
- 1/2 teaspoon kosher salt
- 1/2 cup packed light brown sugar
- 1 teaspoon pure vanilla extract
- 1/2 cup raisins
- 1/2 cup unsalted mixed nuts, such as walnuts and almonds, roughly chopped
- 2 ounces semisweet chocolate, chopped
- Heat oven to 325° F. Line the bottom and sides of a 9-by-13-inch baking pan with aluminum foil; butter the foil.
- In a medium bowl, stir together the oats, flour, baking soda, cinnamon, and salt.
- In a large bowl, using a wooden spoon, mix together the butter, sugar, and vanilla until creamy. Stir in the oat mixture, raisins, and nuts until combined.
- Press the oat-butter mixture evenly into the prepared pan. Bake until the edges are golden, 18 to 20 minutes. While still warm, cut into 15 bars. Let cool completely in the pan.
- Meanwhile, in a double boiler or a medium heatproof bowl set over (not in) a saucepan of simmering water, melt the chocolate, stirring often, until smooth. Drizzle over the cooled bars and chill until set, 15 to 20 minutes.
- Storage suggestion: Keep the bars at room temperature, individually wrapped or between sheets of wax paper in an airtight container, for up to 5 days.