Ingredients

For the base:
• 1 cup (2 sticks / 230g) unsalted butter, softened
• 1 cup (200g) packed brown sugar
• 1 large egg
• 1 tsp vanilla extract
• 1½ cups (190g) all-purpose flour
• 1½ cups (135g) old-fashioned rolled oats
• ½ tsp baking soda
• ¼ tsp salt

For the topping:
• 1 cup (175g) semi-sweet chocolate chips
• 1 cup (100g) chopped pecans or walnuts

Instructions

Preheat oven to 350°F (175°C). Grease a 9×13″ baking pan; line with parchment for easy removal.
Base: In a large bowl, cream butter and brown sugar until light and fluffy (~3 min). Beat in egg and vanilla.
Whisk flour, oats, baking soda, and salt. Gradually add to wet ingredients; mix until just combined.
Press dough evenly into prepared pan. Bake 15–18 min until edges are golden and center is set.
Immediately sprinkle chocolate chips over hot base. Let sit 2–3 min until chips soften, then spread into an even layer with an offset spatula.
Sprinkle chopped pecans evenly over chocolate. Press gently so they adhere.
Cool completely in pan (at least 2 hours). Lift out using parchment; cut into squares.