Mix the graham cracker crumbs, melted butter, and granulated sugar in a bowl until well combined. Press the mixture firmly into the bottom of an 8x8-inch baking pan lined with parchment paper.

In a saucepan over medium heat, combine the sweetened condensed milk, corn syrup, and 3 tablespoons of butter. Stir continuously until the mixture thickens and turns a golden caramel color, which should take about 8-10 minutes. Once done, remove from heat and stir in the vanilla extract and sea salt. Pour the caramel over the prepared crust and spread it evenly. Sprinkle a pinch of sea salt on top.

Melt the chocolate chips either in the microwave or using a double boiler. Pour the melted chocolate over the cooled caramel layer and use a spatula to smooth it out. Sprinkle extra sea salt flakes on top before setting the bars in the fridge for at least two hours.