Step 1: Preheat Oven & Prepare Pan: Preheat the oven to 350°F (175°C). Line an 8x8-inch or 9x9-inch square baking pan with parchment paper, leaving overhang on two sides to act as handles for easy removal later. You can also use aluminum foil sprayed with cooking spray. This step is crucial and makes removing the bars so much easier.
Step 2: Make the Crust Layer: In a food processor, pulse pretzels and graham cracker crumbs until finely crushed. Add melted butter and brown sugar, then pulse again until the mixture resembles wet sand. Press firmly into the prepared pan in an even, flat layer. You want a compact, even layer that won't crumble apart later. Bake in preheated oven for 10-12 minutes until the crust is set and just beginning to turn golden at the edges. Remove from the oven and allow it to cool while preparing the caramel.
Step 3: Make the Caramel Layer: Add 2 tablespoons of heavy cream and soft caramel squares or bits to a microwave-safe glass mixing bowl, microwave for 30 seconds, then stir. Continue to heat and stir in 15-second increments until smooth and slightly thinned, adding an additional tablespoon of heavy cream during the process, if necessary, to achieve a smooth and pourable caramel. *Alternatively, use a double-boiler setup on the stove top. Place soft caramel squares or bits and heavy cream in a heat-safe glass mixing bowl that fits over a saucepan with 1 ½ inches of water. Heat over low, stirring frequently, until completely melted and smooth. This takes about 5 minutes.
Step 4: Pour & Set Caramel Layer: Pour caramel over the slightly cooled crust and use an offset spatula or rubber spatula to spread it evenly to the edges. Sprinkle with flaky sea salt and allow to cool while preparing the chocolate layer. Be sure it is slightly firm to the touch before moving on to the next step and pouring the chocolate layer. Place in the refrigerator or freezer for a few minutes, if necessary, to firm it up.
Step 5: Make the Chocolate Espresso Ganache: Chop chocolate into small, uniform pieces if using chocolate bars instead of chips. Place the chocolate in a heatproof bowl. Heat heavy cream in a small saucepan until it just begins to simmer. You'll see small bubbles around the edges. Do not let it boil. Remove from heat and stir in the espresso powder until dissolved. Pour the hot cream mixture over the chocolate and let it sit for 2 minutes without stirring. This allows the chocolate to melt evenly. After 2 minutes, whisk gently from the center outward until the mixture is completely smooth and glossy. Let the ganache cool for 3 to 4 minutes, stirring occasionally. You want it to thicken slightly but still be pourable. If it gets too thick, you can microwave it for 10-15 seconds to loosen it.
Step 6: Pour & Chill: Pour the chocolate espresso ganache over the caramel layer and gently spread it to the edges with an offset spatula. If you want a perfectly smooth top, tilt the pan slightly in different directions to let the ganache self-level. Cover the pan with plastic wrap (don't let it touch the chocolate surface) and refrigerate for at least 2-3 hours, or preferably overnight. The bars need this time to set properly.
Step 7: Slice & Serve: When you're ready to serve, use the parchment paper overhang to lift the bars out of the pan and onto a cutting board. Allow them to come to room temperature for 15 to 20 minutes before cutting. For the cleanest cuts, dip a sharp knife in hot water, wipe it dry, and then make your cut. Repeat this process for each slice. Cut these into 16 squares for generous portions, or 25 smaller squares if serving them as part of a dessert table. They're very rich, so a little goes a long way!