Chill the unchopped candy for 30–60 minutes. Combine the flour, baking soda, and salt in a bowl. Line two baking sheets with parchment paper.

Beat the softened butter and sugars until smooth. Add the egg and vanilla and beat just until combined. Mix in the dry ingredients until a dough forms.

Fold in the chopped candy. Scoop 1½–2 Tbsp portions onto the prepared baking sheets, spacing them 3–4 inches apart. Press soft caramel pieces into the tops only, if using.

Bake one sheet at a time at 350°F for 8–10 minutes, until the edges are set and slightly golden while the centers remain soft. Cool on the baking sheet for 5 minutes, then transfer to a rack.