In a mixing bowl, whisk together the flour, cocoa powder, powdered sugar, and salt.

Add the cold, cubed butter and mix until the mixture resembles coarse crumbs.

Stir in the beaten egg and vanilla extract until the dough comes together.

Wrap the dough in plastic wrap and refrigerate for about 30 minutes.

While the dough chills, preheat your oven to 350°F (175°C).

On a floured surface, roll out the chilled dough to about 1/8 inch thickness.

Use a round cookie cutter to cut out circles (about 3-4 inches in diameter). Gently press each circle into a taco shell mold or an upside-down muffin tin.

Bake in the preheated oven for 10-12 minutes, or until the edges are firm.

Let them cool completely in the molds to hold their shape.

In a mixing bowl, beat the softened cream cheese until smooth. Then, add the powdered sugar, cocoa powder, and vanilla extract, mixing until well combined.

Gently fold in the whipped heavy cream until the mixture is light and fluffy.

Once the taco shells are cool, fill each shell with the chocolate cheesecake filling using a piping bag or spoon.

Drizzle with chocolate sauce and top with whipped cream and chocolate shavings or sprinkles, if desired.

Serve immediately or refrigerate until ready to serve.