Preheat the oven to 350 degrees F (175 C).

Mix flour, softened butter, and sugar together in a medium bowl until well blended and crumbly. Press into the bottom of a 9-inch square baking pan.

Bake in the preheated oven until dry and light golden brown, about 20 minutes.

Bring butter, brown sugar, condensed milk, and corn syrup to a boil in a saucepan over medium-low heat. Boil for 5 minutes, then remove from the heat and beat vigorously with a wooden spoon for about 3 minutes.

Pour caramel mixture over baked crust and let sit at room temperature until caramel begins to firm up, 2 to 3 hours.

Microwave chocolate in a microwave-safe bowl on high for 1 minute, then stir. Continue to heat and stir in 20-second intervals until chocolate is melted and smooth.

Pour chocolate evenly over caramel layer and chill in the refrigerator until completely set, about 30 minutes.