Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone mat. Arrange 40 buttery round crackers in a tight, even layer.
In a medium saucepan over medium heat, melt 1 cup (2 sticks) of unsalted butter. Add 1 cup packed brown sugar and 1 teaspoon vanilla extract.
Stir constantly until smooth and bubbling. Let it boil for 3–4 minutes, stirring the whole time, until thickened.
Carefully pour the hot caramel over the crackers. Use a spatula to spread it out evenly, covering every cracker.
Bake for 5 minutes. The caramel should bubble—this means it’s setting.
Remove the tray from the oven and sprinkle 1 cup semi-sweet chocolate chips evenly over the caramel. Let sit for 2–3 minutes, then spread into a smooth layer with a spatula.
While the chocolate is still warm, lightly sprinkle sea salt across the top. Let the tray cool completely, then break into bite-sized pieces and enjoy.