Sift together the powdered sugar, almond meal, and cocoa so there are no lumps.  Sift again discarding any large almond pieces.  Set aside.

In the bowl of a stand mixer beat the egg whites until they hold their shape.  Continue whipping while adding the granulated sugar a little at a time.  Beat until the meringue is very stiff and firm.

Carefully fold in half the dry ingredients into the egg whites with a rubber spatula.  Do not beat but blend until creamy and smooth.  Add the remaining dry ingredients and fold gently until mixed.  Spoon the batter into the pastry bag.  Pipe the batter on the parchment lined baking sheets in 1-inch circles evenly spaced about 1-inch apart.

Rap the baking sheet on a firm counter a few times to flatten the batter a bit.  Bake for 15-18 minutes.  Cool completely on the baking sheet before filling.

To make the chocolate filling, mix the cream and corn syrup together in a small saucepan.  Heat until the cream begins to boil.  Remove from heat and dump in the chocolate chips.  Set aside for 1 or 2 minutes to begin melting the chocolate.  Stir until the chocolate in completely melted then add the butter.  Stir until blended.  Cool the filling completely before using.

Spread about 1 teaspoon filling on the inside of one macaron.  Sandwich another cookie on top and twist them slightly to spread the filling evenly.  Store in an airtight container in a cool place.  Let the macarons sit for one day before serving, to meld the flavors.