Preheat oven to 350 degrees.Combine together cookie crumbs, melted butter, and 3 tablespoons sugar in a bowl. Press crumb mixture onto bottom and up 1 inch on sides of a 9-inch pan. Bake about 10 minutes. Transfer to a wire rack, and let cool. Reduce oven temperature to 300° F.
Melt chocolate in a medium heatproof bowl set over a pan of simmering water or into the microwave, stirring, about 2 minutes. Let cool.
Put cream cheese in the bowl of an electric mixer with the paddle attachment on; mix on medium speed until fluffy, about 3 minutes. Mixing on low speed, add remaining cup sugar ilittle by little. Add salt, mix until combined. Add sour cream, cocoa, vanilla, and melted chocolate; mix until combined. Add eggs, one at a time, mixing each until just combined (do not overmix). Pour cream cheese filling over crust.
Bake until set but still wobbly in center, 50 to 60 minutes. Let cool completely in the pan on rack. Refrigerate, uncovered, 6 hours or overnight. Before unmolding, run a knife around edge of cake.