Using a stand mixer, cream together the butter and sugars until light in color and fluffy in texture.
Add in the eggs, corn syrup and 1 tbsp of vanilla. Mix until thoroughly combined.
Next, add the flour, cocoa, cornstarch baking soda and salt. Mix until your chocolate cookie dough forms. The dough will be soft.
Divide the dough out into 12 equal portions, I like to use my 1/2 cup measuring cup to help divide the dough. You'll want to use a little less than 1/2 cup of dough to have 12 cookies.
Roll each portion onto a ball then flatten slightly so it looks like a hockey puck before arranging on a parchment paper or silicone mat covered pan. Place 6 cookies per tray.Bake at 350° for 15-17 minutes. The cookie should start to crack and crinkle, it will spread slightly and the centers of the cookie should no longer look wet before taking them out of the oven.
Right after the cookies come out of the oven, spoon about a tbsp or so of sweetened condensed milk onto each cookie. It will drip down the sides, which is why we wanted a silicone mat or parchment paper! Just let that cookie soak up the sweetened condensed milk.
Repeat with each cookie and then allow the cookie to cool completely.
Once the cookies are cool, make the frosting. Make the frosting by adding the heavy whipping cream to either the bowl of your stand mixer or a large bowl that you can use an electric hand mixer with.
Whip the cream on medium high speed until it starts to thicken.
Once it starts to thicken, slow the speed down and gradually add in the powdered sugar and vanilla. Once all of the powdered sugar has been added bump the speed up to as high as it can go and whip it until stiff peaks form. Once stiff peaks form, the frosting is done!
Add the frosting to a piping bag with a large closed star tip. Zig zag the frosting across the cookies from side to side to cover the top of the cookie and then sprinkle the heath bits on top.
Repeat with all of the cookies and then chill in the fridge for 30 minutes before serving.
Serve chilled and store in the refrigerator.
Cookies store really well in the fridge and can be made a few days in advance if needed.