Preheat the oven to 350 degrees F (175 degrees C).
Step 2
Mix together graham cracker crumbs, melted butter, and 2 tablespoons sugar in a medium bowl until well combined. Press mixture into the bottom and 2 inches up the sides of a 9-inch springform pan. Place in the refrigerator for crust to set.
Step 3
Place chocolate chips in the top of a double boiler over simmering water. Stir frequently, scraping down the sides with a rubber spatula to avoid scorching, until chocolate is melted, about 5 minutes. Set aside.
Step 4
Beat together cream cheese and 1 cup sugar in a large bowl until smooth and creamy. Blend in eggs one at a time, mixing after each addition until just incorporated. Gradually pour in melted chocolate, beating on low speed until well blended. Add 1/2 cup sour cream, flour, and vanilla. Blend until smooth, then pour into crust.
Step 5
Bake in the preheated oven until center is set and filling is firm, 55 to 60 minutes. Turn the oven off. Cool cheesecake in the oven for 1 hour without opening the door. Remove cheesecake to the counter and cool completely at room temperature. Transfer cheesecake to the refrigerator and chill for several hours to overnight.
Step 6
Stir together 1/2 cup sour cream and 1 tablespoon sugar in a small bowl until well combined. Spread over chilled cheesecake before serving.