Combine graham cracker crumbs, sugar, and melted butter in a mixing bowl, stirring until evenly coated and resembling damp sand.
Press this crumb mixture firmly into the bottom of your square pan, smoothing the surface with the back of a spoon or a flat-bottomed glass. Chill in the fridge for 15 minutes to set.
In a saucepan over low heat, melt the sweetened condensed milk, stirring constantly until it thickens slightly and turns a light golden color, about 5-7 minutes. The smell should be sweet with a toasted note.
Remove the caramel from heat and stir in vanilla extract and sea salt flakes, blending until smooth and glossy.
Pour the warm caramel evenly over the chilled crust, spreading gently with a spatula to create a smooth, uniform layer.
Return the pan to the fridge and chill for at least 2 hours, or until the caramel layer is firm and slightly jiggly but not sticky to touch.
Melt the dark chocolate in short bursts in the microwave until glossy, then drizzle it over the set caramel layer for a beautiful finish.
Sprinkle flaky sea salt flakes over the chocolate for a satisfying crunch and contrast.
Refrigerate for another 15-20 minutes until the chocolate drizzle sets completely.
Remove from the fridge and let sit at room temperature for about 10 minutes. Use a warmed, sharp knife to cut into small squares or bars for serving.
Enjoy these rich, chewy caramel bars with a crispy crust and a salty-sweet finish. Keep leftovers in an airtight container in the fridge for up to a week.
