Classic shortbread cookies recipe upgraded with toffee pieces and dipped in dark chocolate with a sprinkling of flaky sea salt.
Preheat oven to 350° F.
Place flour, brown sugar, cornstarch, and salt in a food processor and blend briefly to combine. Place butter pieces and vanilla in the food processor and pulse until mixture resembles a fine meal. Add toffee pieces and briefly pulse until mixed through.
Transfer the dough to a large piece of wax paper and top with another sheet of wax paper. The dough at this point is extremely crumbly. Fold the dough over onto itself 2-3 times in the wax paper so that the butter melts a bit and brings the dough together. Roll dough out until 1/4" thick*.
Using a 2" circular cookie cutter (or the shape of your choice) cut out as many cookies as possible. Transfer cookies to a baking sheet (lined with non-stick paper, but ungreased), spacing about 1". Gather scraps together, preroll and cut out more cookies. Repeat until dough has been used up.
Bake cookies until just starting to colour, about 8-15 minutes. Let cool for 5 minutes then transfer to a wire rack to cool completely.
Once cookies are completely cooled, melt chocolate pieces in short bursts (20-30 seconds) in the microwave. Dip cooled cookies part way into the melted chocolate. Place on a wire rack and lightly sprinkle with flaky sea salt.
Cookies will keep for up to 5 days in an airtight container.
* I rolled the dough out, cut out cookies from the middle, less crumbly section and then rolled the rest back together to form the dough properly. I do this 3-5 times depending on how well the cookie dough comes together.