Preheat oven to 350°F and line two baking sheets. Brown the butter in a saucepan over medium heat, swirling often, until amber and nutty. Pour into a bowl and cool 10 minutes.

Whisk brown sugar and granulated sugar into the cooled butter until sandy, then whisk in egg and vanilla until thick.

Whisk flour, baking soda, and salt together. Fold into the wet mix until just combined.

Chop candy into pea- to grape-sized pieces, then fold into the dough.

Scoop 1½-tablespoon portions onto sheets, spacing 2 inches apart. Bake 11 to 13 minutes until edges are set and centers look soft. Cool on the sheet 3 minutes, then move to a rack.