Line a small baking sheet (9×13) with parchment paper or a silicon mat and set aside.
In medium heavy saucepan (I used a 3-quart) with a candy thermometer attached, melt butter, brown sugar, white sugar, molasses, salt and espresso together over together. Cook over medium heat, stirring occasionally with a whisk (one that reaches into the corners is especially helpful here) until the temperature approaches 250-F, at which point you should stir constantly until it reaches 300-F.
Pour immediately into the prepared baking sheet – you can spread it more evenly with an offset or silicon spatula but don’t worry if you have neither. Sprinkle the chocolate chips over the toffee and let them sit for a minute until soft, then spread the chocolate evenly over the candy base. Sprinkle the chocolate with chopped hazelnuts and then you can slide the sheet onto a cooling rack in the freezer until the toffee is set.
Break into pieces and store in an airtight container. If you’re kitchen runs warm, you might prefer to keep it in the fridge so the chocolate doesn’t get soft.