In a heavy saucepan, combine sweetened condensed milk, unsalted butter, light brown sugar, and light corn syrup. Heat over medium heat until bubbling, then reduce to a simmer. Stir continually for about 5-7 minutes until the mixture thickens. Remove from heat and mix in vanilla extract and fine salt. Allow the caramel to cool slightly before setting aside while you prepare the crust.

Preheat your oven to 350°F (175°C). In a mixing bowl, combine unsalted butter, all-purpose flour, powdered sugar, and fine salt until the mixture resembles coarse crumbs. Press this mixture firmly into the bottom of an 8x8-inch baking pan, using a fork to prick the surface. Bake for 22-25 minutes, or until the edges are golden brown. Let the crust cool for a few minutes before adding the brownie batter.

In a large bowl, whisk together granulated sugar, all-purpose flour, unsweetened cocoa powder, powdered sugar, chocolate chips, and fine salt. In a separate bowl, whisk together large eggs, vegetable oil, melted unsalted butter, water, and vanilla extract until smooth. Gently combine the wet and dry ingredients until just blended, ensuring not to overmix. Pour this luscious brownie batter over the cooled shortbread crust.

Lower the oven temperature to 325°F (163°C) and bake the Millionaire Brownies for 38-43 minutes. You’ll know they’re done when the edges are set but the center has a slight jiggle. Remove from the oven and let them cool completely on a wire rack, or for a quicker option, place them in the freezer for about 30 minutes to firm up.

In a small saucepan, heat heavy cream over medium heat until it begins to bubble. Pour the hot cream over the dark chocolate chips in a mixing bowl and allow it to sit for about 1 minute. Stir gently until the chocolate is fully melted and the ganache is smooth. Add in softened unsalted butter and light corn syrup, then let the ganache cool to room temperature before spreading it over the brownies.

Once the brownies have cooled completely, spread the cooled caramel evenly over the brownie layer. Next, gently pour the chocolate ganache on top, using a spatula to ensure an even layer. For the final touch, sprinkle flaky sea salt over the ganache. Allow everything to set before cutting into square pieces with a warm knife for clean slices.