Preheat oven to 350°F Butter the side of a 9-inch springform pan.
Make the crust: In a food processor, grind the crackers fine. Add the butter, and sugar and pulse the motor until thoroughly combined. Pour the crumbs into the prepared pan and press them onto the bottom and 1 inch up the side of the pan. Bake in the middle of the oven for 15 minutes. Let cool.
With an electric mixer fitted with flat beater, beat the cream cheese and sugar on low until smooth. In another bowl whisk together the eggs, yolks, and vanilla, add to the batter and beat until smooth, scraping the bowl. Add the chocolate and beat until smooth, scraping the bowl. Stir in the liqueur and pour batter into the pan.
Bake in the middle of the oven for 55 minutes. The center of the cake will appear unset.
Immediately run a thin knife around the edge of the pan to release the cake and let it cool completely in the pan. Chill the cake for at least 4 hours or until chilled throughout. Remove the side of the pan and serve.