Place the sugar, butter, cocoa, and salt in a large microwave-safe bowl, and microwave in one-minute increments, stirring, until the butter is completely melted and the mixture feels very warm to the touch.

Stir in the egg vigorously.

Fold in the flour.

Stir in the vanilla.

Preheat the oven to 350 degrees, and line baking sheets with parchment.

Cream the butter and sugar, just until smooth and combined.

Mix in the egg until incorporated.

Stir in the vanilla.

Add the cornstarch and salt, and mix on medium-low speed.

Stir in the flour, 1/2 cup at a time.  Stop adding flour when the dough gathers itself into a ball and pulls away cleanly from the sides of the bowl.

Roll the dough out between 2 sheets of parchment paper, to a thickness of 1/8 inch.*

Use a 3-inch diameter cookie cutter to cut circles.

Place a scant tablespoonful of fudge brownie filling in the center of each circle, and fold 3 sides of the circle inward to create a triangle.

Pinch the corners to seal them, and bake for 20 to 25 minutes, or until just beginning to turn golden around the edges.