Step 1: Prepare the Crust

1. Preheat your oven to 350°F (175°C) and line a 9×13-inch baking dish with parchment paper.
2. In a mixing bowl, combine flour, softened butter, sugar, and salt.
3. Mix until the dough resembles coarse crumbs.
4. Press the dough evenly into the prepared baking dish.
5. Bake for 15-18 minutes or until golden brown.
6. Remove from the oven and let it cool slightly.

Step 2: Make the Dark Chocolate Filling

1. In a saucepan over medium heat, warm the heavy cream and butter until it starts to simmer.
2. Remove from heat and add the dark chocolate chips.
3. Let it sit for a minute, then stir until smooth.
4. Mix in vanilla extract and cocoa powder.
5. Pour the chocolate mixture over the cooled crust and spread evenly.

Step 3: Prepare the Raspberry Topping

1. In a saucepan, combine raspberries, sugar, cornstarch, water, and lemon juice.
2. Cook over medium heat until the mixture thickens and becomes jam-like.
3. Remove from heat and let it cool for a few minutes.
4. Spread the raspberry mixture evenly over the chocolate layer.

Step 4: Chill and Set

1. Place the baking dish in the refrigerator for at least 3 hours or until fully set.
2. Once set, remove from the fridge and lift the bars out using the parchment paper.
3. Slice into squares or bars and serve.