To make the filling, combine 1 1/2 cups sugar, the cocoa powder, 2 teaspoons instant coffee, and the cornstarch in the bowl of an electric mixer; stir until blended. Add the softened cream cheese and beat until the sugar mixture has been incorporated and no lumps of cream cheese remain. Beat in the eggs, one at a time, adding the vanilla extract with the last egg. Fold in 1/2 cup of chopped pecans, then pour into the prepared crust.