Prep the pan: Heat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving an overhang on two sides for easy lifting.

Make the base: In a bowl, mix 1 cup flour, 1/3 cup granulated sugar, and 1/4 teaspoon fine sea salt. Melt 1/2 cup (1 stick) unsalted butter, then stir it in until the mixture looks like damp sand. Press evenly into the pan.

Bake the base: Bake 16–18 minutes, until the edges are lightly golden. Set aside to cool slightly while you make the caramel.

Start the caramel: In a medium, heavy-bottomed saucepan, combine 1/2 cup unsalted butter, 1/2 cup light brown sugar, 1/2 cup granulated sugar, 1/4 cup corn syrup (optional), and a pinch of salt. Cook over medium heat, stirring until the butter melts and everything looks glossy.

Cook to color: Bring to a gentle bubble and cook 4–6 minutes, stirring often, until the caramel turns a deep honey color and thickens slightly. It should coat the back of a spoon.

Finish with cream: Carefully whisk in 1/2 cup heavy cream. The mixture will bubble up—keep whisking until smooth. Cook 1–2 minutes more, then remove from heat and stir in 1 teaspoon vanilla.

Assemble: Pour the caramel over the warm base and tilt the pan for an even layer. If using, sprinkle a little flaky sea salt on top.

Set and slice: Let the pan cool at room temperature for 45–60 minutes, then chill 20–30 minutes to firm. Lift out using the parchment and slice into small squares with a sharp knife.

Serve: Enjoy at room temperature for ultimate stickiness or slightly chilled for cleaner edges.