Prepare Caramel Filling: In a medium saucepan, combine sweetened condensed milk, unsalted butter, brown sugar, and light corn syrup. Cook over medium heat, stirring constantly until bubbling, then reduce heat and simmer for about 5-7 minutes until thickened. Remove from heat and stir in vanilla extract and fine salt. Let cool.

Make Shortbread Crust: Preheat oven to 350°F (175°C). In a mixing bowl, combine butter, all-purpose flour, powdered sugar, and a pinch of salt. Mix until crumbly, then press into the bottom of an 8x8-inch pan. Bake for 22-25 minutes until lightly browned. Cool and reduce oven to 325°F (163°C).

Mix Brownie Batter: In a large bowl, combine granulated sugar, all-purpose flour, cocoa powder, powdered sugar, dark chocolate chips, and fine salt. In another bowl, whisk eggs, vegetable oil, melted butter, water, and vanilla. Fold wet into dry until just combined.

Bake Brownies: Pour brownie batter over cooled shortbread crust. Bake at 325°F (163°C) for 38-43 minutes until edges are set. Cool completely.

Prepare Ganache: Heat heavy cream over medium heat until bubbling. Pour over dark chocolate chips in a bowl and let sit. Stir until smooth and glossy, then mix in unsalted butter and a sprinkle of salt. Cool to room temperature.

Assemble: Once brownies are cool, pour caramel layer evenly over the brownie base. Spread ganache on top and sprinkle with flaky sea salt. Chill for better slicing.