Step 1: Prepare the Crust - Preheat your oven to 350°F (175°C). In a food processor, crush the graham crackers until you have fine crumbs. Add the melted butter, cocoa powder, and brown sugar to the crumbs, and pulse until combined. Press this mixture into the bottom and up the sides of a 9-inch tart pan. Bake the crust for 10 minutes, then remove it from the oven and allow it to cool.
Step 2: Make the Chocolate Fudge - In a small saucepan over low heat, combine the chopped chocolate, 2 tablespoons of butter, 1/3 cup of milk, and 1/4 teaspoon of salt. Stir continuously until everything is melted and smooth. Remove from heat and mix in 2 teaspoons of vanilla extract. Set aside to cool slightly.
Step 3: Prepare the Lemon Ricotta Filling - In a mixing bowl, combine the ricotta cheese, softened mascarpone cheese, granulated sugar, eggs, lemon zest, and lemon juice. Use a whisk to mix until everything is well combined and smooth. Add the remaining 2 teaspoons of vanilla extract to the mixture.
Step 4: Combine and Swirl - Take the prepared chocolate fudge and add half of it to the lemon ricotta mixture. Gently fold it in to create a marbled effect. Pour the ricotta filling into the cooled graham cracker crust, then drizzle the remaining chocolate fudge on top. Use a knife or skewer to swirl the chocolate into the filling.
Step 5: Bake the Tart - Bake the tart in the preheated oven for 30-35 minutes, or until the filling is set but still slightly jiggly in the center. Remove from the oven and let it cool completely at room temperature. Once cooled, refrigerate for at least 2 hours before serving.
Step 6: Serve and Enjoy - Before serving, you can top the tart with whipped cream and decorate with thin slices of lemon for a beautiful presentation. Slice into wedges and enjoy the harmonious blend of flavors in this Chocolate Fudge Swirled Lemon Ricotta Tart!