Heat oven to 350°F. Line an 8-inch square pan with parchment and lightly grease.
Whisk melted butter with brown sugar and granulated sugar until glossy and smooth.
Beat in eggs, one at a time, then stir in vanilla until combined.
In a bowl, whisk flour, baking powder, and salt. Fold the dry mix into the wet just to combine.
Gently fold in butterscotch chips and nuts if using. Do not overmix.
Spread the thick batter into the pan and smooth the top.
Bake 23–27 minutes, until the edges are set and a toothpick shows a few moist crumbs.
Cool completely in the pan on a rack. Lift out using parchment and slice into squares.
Serve as is, or warm briefly and drizzle with extra butterscotch sauce.
Notes
Swap half the butterscotch chips for white chocolate or add a sprinkle of flaky salt before baking. Store airtight at room temperature up to 3 days, or freeze bars well-wrapped for 2 months.This recipe is an original creation inspired by classic Butterscotch Brownies Delight flavors. All ingredient ratios and instructions are independently developed.