In the bowl of an electric mixer fitted with the paddle attachment, cream together the butter, granulated sugar and brown sugar until light and fluffy, scraping the sides of the bowl as necessary.
Add in the eggs, one a time, mixing thoroughly after each addition. Add vanilla and mix to combine.
In a separate bowl, sift together the cocoa powder, flour, baking soda, baking powder and salt. Slowly add the flour mixture into the butter mixture. Mix until fully incorporated.
Remove dough from bowl and pat into 2 round discs of equal size. Wrap in plastic wrap and refrigerate for at least one hour.
When ready to bake, preheat oven to 350° F and grease two cookie sheets or line with parchment paper.
Remove one disc of dough from the refrigerator. Roll dough into balls about 1 ½” in diameter. Roll in the remaining granulated sugar so they are fully coated. With your thumb, create an indent on the top of the cookie and place on cookie sheet. Continue until sheets are full and place any remaining dough back into the refrigerator.
Fill each indent with about 1 teaspoon of mint jelly. Place in the oven and bake for 12-14 minutes, until cookies have set and jelly has melted.
Allow the cookies to cool on the cookie sheets for 5 minutes and then move to a wire rack to cool completely. Repeat with remaining cookie dough.
When the cookies have cooled completely, slightly warm the Bittersweet Chocolate Sauce in the microwave. When pourable, spoon the chocolate sauce over the mint jelly to fill in the rest of the indent. Allow the chocolate sauce to set before serving.