Adapted from Giada de Laurentiis
Place an oven rack in the center of the oven and preheat to 350°F. Line an 8-inch square pan (or similar size) with parchment paper, allowing excess to hang over the sides.
Melt 1 stick of the butter in the microwave or in a saucepan. In a food processor, pulse the graham crackers and 1/4 cup of the brown sugar until the mixture resembles fine bread crumbs. Add the melted butter and blend until all combined. Spread the mixture into the bottom of the prepared pan, pressing into an even layer.
Bake for 10-12 minutes or until edges of the crust are golden brown. Cool at room temperature for 10 minutes. (If in a hurry, place in the fridge to cool.)
In a saucepan, combine half of the heavy cream (1/2 cup), remaining butter (1 stick), and remaining brown sugar (1 1/2 cups), along with 1 tablespoon of water. Stir over medium heat until the mixture is smooth. Bring the mixture to a boil and cook, without stirring, until a candy thermometer registers 240°F, about 5-7 minutes.
Remove from heat and carefully pour caramel over the cooled crust. Cool and set at room temperature (about 30 minutes).
Combine chocolate chips and remaining heavy cream (1/2 cup) in a double boiler, or in heat-proof bowl over simmering water. (Make sure the bowl does not touch the water.) Stir until the chocolate is melted and smooth, about 3 minutes.
Whisk in the espresso powder and stir until combined. Pour chocolate mixture over the cooled caramel layer and smooth the edges with a spatula. Allow chocolate to harden at room temperature, 1-2 hours. (Can place in fridge to speed up the process.) After an hour or so, top with sea salt.
After cooled and set, lift the bars out of the pan using the parchment paper. Run a sharp knife under hot water and carefully cut into 1 inch squares. Store in airtight container in fridge.
Before serving, allow the bars to come to room temperature, or about 1-2 hours.