Combine graham cracker crumbs, 2 tablespoons sugar, and melted butter.

Press mixture evenly on bottom of an ungreased 9-inch springform pan; set aside.

Bring 1 cup water to a boil in a small saucepan.

Add ground espresso to boiling water; reduce heat to medium and simmer for 1 minute.

Pour the espresso mixture through a fine wire-mesh strainer into a bowl; discard the grounds.

Reserve 9 tablespoons of the coffee liquid.

In a microwave-safe bowl, combine 7 tablespoons of the reserved coffee, semi-sweet chocolate chips, and 1/3 cup of sweetened condensed milk.

Microwave on 100% power for 1-2 minutes or until chocolate is melted.

Stir the chocolate mixture until smooth.

Set the chocolate mixture aside.

Beat cream cheese and the remaining 1 cup of sugar until fluffy.

Add eggs, one at a time, beating just until blended.

Stir in the chocolate mixture and sour cream.

Pour the cheesecake filling into the prepared graham cracker crust.

Bake in a preheated 350°F (175°C) oven for 45 minutes.

Turn the oven off, remove the cake from the oven, and gently run a knife around the edge of the pan to release the sides.

Return the cake to the oven and let stand with the door partially open for 1 hour.

Remove the cake from the oven.

Cover and chill the cheesecake thoroughly.

Combine the remaining sweetened condensed milk, the remaining 2 tablespoons of coffee, and coffee liqueur.

Serve the cheesecake with the coffee liqueur sauce.