Preheat your oven to 350°F (175°C) and line an 8-inch square pan with parchment paper.
For the crust, mix the softened butter, powdered sugar, flour, and toasted pecans until combined and press firmly into the bottom of the prepared pan.
Bake the crust for 15-20 minutes or until lightly golden, then set aside to cool.
To make the caramel, melt the butter in a saucepan over medium heat until it browns slightly, then stir in the sweetened condensed milk, brown sugar, and corn syrup.
Cook the caramel mixture, stirring constantly, until it thickens and turns a deep golden amber color, then remove from heat and stir in the vanilla extract.
Pour the hot caramel evenly over the cooled crust and refrigerate for 30-60 minutes until set.
For the ganache, heat the whipping cream until simmering, pour it over the chopped dark chocolate, and let sit for 2 minutes before whisking until smooth.
Pour the ganache over the set caramel layer, sprinkle with flaky sea salt, and refrigerate until fully firm.
Slice into squares and serve chilled.