In a medium bowl, combine the chocolate cookie crumbs, ¼ cup granulated sugar (for crust), and melted butter. Mix until the mixture forms a paste.
Press the mixture firmly into a 9-inch springform pan, creating an even crust. Chill in the refrigerator for at least 20-30 minutes.
In a large mixing bowl, beat the softened cream cheese with ⅔ cup granulated sugar (for filling) and 1 ½ teaspoons vanilla extract until smooth and creamy.
Mix in the unsweetened cocoa powder until fully incorporated.
In a separate bowl, whip the heavy cream until stiff peaks form.
Gently fold the whipped cream into the cream cheese mixture until fully combined and no streaks remain.
Spread the cream cheese filling over the chilled crust and smooth the top. Chill for at least 2 hours to allow the layer to firm up.
For the ganache, heat ½ cup chocolate pieces with 2 tablespoons plant-based or regular milk in a microwave-safe bowl until melted and smooth, stirring occasionally. Alternatively, use a double boiler on the stovetop.
Pour the melted chocolate ganache over the cream cheese layer and spread it evenly over the top. Chill the cheesecake for at least 4 hours, or until fully set.
Once set, remove the sides of the springform pan and transfer the cheesecake to a serving plate. Garnish with chocolate shavings or sprinkles, if desired. Slice and serve.