Preheat your oven to 300°F (about 150°C). Line your baking sheets with parchment paper to prevent sticking and ensure even baking.

Cut the cold butter into chunks and place in the bowl of a stand mixer (or a large mixing bowl if mixing by hand). Add the sugar. Cream the butter and sugar together until fairly smooth and light — but because the butter is cold the mixture will remain quite firm.

Add the vanilla extract and mix until incorporated.

In a separate bowl combine the flour and salt. Gradually add the flour mixture to the butter‑sugar mixture. Mix just until a stiff dough forms. Do not overmix. The dough will appear dry and firm.

Add the toffee bits to the dough. Use the mixer at low speed to begin incorporating them, then finish by hand to ensure the toffee bits are evenly distributed without crushing them. The dough will become slightly softer but still firm.

Use a small cookie scoop (about 1¾ inch) or lightly over one tablespoon of dough to form evenly sized cookie balls. Roll each ball between your palms until smooth and round. Place the balls on the parchment-lined baking sheets about 2 inches apart.

Flatten each ball gently using a cookie stamp dipped in granulated white sugar, or the bottom of a glass. The sugar will help prevent sticking and add a delicate sparkle.

Bake in the preheated oven for 18 to 22 minutes. Check the cookies around 18 minutes — the edges should be set but the centers should still look slightly soft. They will firm up as they cool.

Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.