Preheat oven to 300°.

To prepare crust: In a small bowl, combine graham cracker crumbs, sugar, and melted butter, stirring to combine well. Press mixture into bottom of 2 (4x1 3/4-inch) heart-shaped springform pans. Bake for 6 minutes.

To prepare filling: In a small bowl, combine chocolate and butter. Microwave on High in 30-second intervals, stirring between each, until chocolate is melted and smooth (about 1 minute total). Let cool slightly.

In a medium bowl, combine cream cheese, sugar, and cocoa. Beat at medium speed with a mixer until creamy. Add egg and egg yolk, beating until combined (do not overbeat). Add melted chocolate mixture, sour cream, and vanilla extract, beating until just combined. Spoon batter into prepared crusts. Bake for 40 to 42 minutes, or until centers are almost set; let cool completely. Refrigerate for 4 hours to overnight. Gently run a knife around edges of pans to release sides. Garnish with raspberries and mint leaves, if desired.