1/2 cup (1 stick) unsalted butter, room temperature, plus more for pan
1/2 cup packed light-brown sugar
1 large egg
1-1/2 cups Everyday Baking Mix, spooned and leveled
1 cup old-fashioned rolled oats (not quick-cooking)
Preheat oven to 350°F. Brush an 8-inch square baking pan with butter. Line bottom and two sides with a strip of parchment paper, leaving a 2-inch overhang on both sides. Butter paper, and set pan aside.
Using an electric mixer, beat butter and sugar until light and fluffy. Add egg, and beat until combined. With mixer on low, gradually add Baking Mix; mix just until combined. Mix in 3/4 cup oats. Pour batter into prepared pan.
Using an offset metal spatula or table knife, smooth batter evenly. Sprinkle with remaining oats, pressing gently to adhere. Bake until a toothpick inserted in center comes out with only a few moist crumbs attached, 30 to 35 minutes. Let cool in pan 30minutes. Using overhang, transfer blondie (still on paper) to a wire rack to cool completely. Place on a cutting board (peel off paper); using a serrated knife, cut into 16 squares. Store blondies in an airtight container at room temperature for up to 2 days, or freeze for up to 2 months.