• Whisk the flour, cocoa, and salt together in a medium bowl. Add 1 cup of the toffee chips and toss with the flour mixture.
• In a separate large bowl beat the butter and granulated sugar together on medium speed about 2 minutes. Scrape down the sides of the bowl.
• Beat in the egg and vanilla.
• Add the flour mixture and mix with a spoon, once it thickens up you can gently knead it to evenly disperse the toffee chips.
• Roll the dough into 1-inch balls and place on a large parchment lined baking sheet. Use your thumb or the end of a wooden spoon or ice cream scoop to press a well into the center of each one.
• Refrigerate the cookies at least 30 minutes.
• Preheat the oven to 350 degrees F. Line a baking sheet or two with silpats or parchment and set cookies on it an inch apart (return the remaining unbaked cookies back to the fridge).
• Bake 8 - 9 minutes. Press the end of a wooden spoon or cookie scoop into the well in the center again, if needed.
• Cool completely on the baking sheet then transfer to wire racks. Repeat until all the cookies are baked.

Make the filling:

• Place the chocolate chips and butter in a small heat-proof bowl.
• Heat the heavy cream in a small saucepan over medium – high heat, stirring often, until it comes to a boil.
• Pour over the chocolate chips and cover the bowl tightly with aluminum foil. Let it sit five minutes.
• Whisk until the chocolate is completely melted and smooth.
• Add the sugar and whisk until smooth and creamy.
• Spoon into the wells of the cookies and sprinkle with the remaining toffee chips. Let set about 1 hour.
• Store well covered in a cool, dry place up to 1 week.