In a medium-sized bowl, stir together the crumbs, sugar, and cinnamon. Add the butter and mix until well combined. Press the mixture on the bottom and halfway up the sides of a 9-1/2-inch springform pan. Chill.

Preheat oven to 275° F. In a food processor, finely chop the chocolate chips. In a large bowl, cream the cream cheese with an electric mixer until smooth. Add the 1-3/4 cups sugar, the flour, and vanilla and beat until well combined. Add the eggs, one at a time, beating well after each addition. Stir in the chopped chocolate, half-and-half, and liqueur.

Pour the batter into the chilled crust and bake in the center of the oven for 2 hours 30 minutes. Remove and let cool in the pan on a wire rack. Chill, covered, overnight.

Release the sides of the pan and place the cake on a serving plate. Serve at room temperature.