01 - Preheat the oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a small saucepan, combine strawberries, sugar, and lemon juice. Cook over medium heat for 5–7 minutes, stirring occasionally, until strawberries break down and mixture thickens. Mash with a fork or blend until smooth. Set aside to cool.
03 - In a microwave-safe bowl, melt butter and chocolate in 30-second intervals, stirring until smooth. Let cool slightly.
04 - Whisk in sugar, eggs, vanilla, and salt until glossy and well combined.
05 - Sift in flour and cocoa powder; fold gently until just incorporated.
06 - Spread brownie batter evenly in the prepared pan.
07 - Drop spoonfuls of strawberry puree over batter. Use a skewer or knife to gently swirl puree into brownie mixture for a marbled effect.
08 - Bake for 28–32 minutes, or until a toothpick inserted in center comes out with a few moist crumbs.
09 - Cool completely in pan, then lift out and cut into squares.