Cream butter, sugar, and vanilla in a large bowl with a hand mixer or stand mixer fitted with the paddle. Beat until very light and fluffy — about 3–5 minutes.

Reduce mixer speed. Add flour and salt in two additions and gently fold until nearly combined and sandy. Avoid overmixing.

Fold in toasted pecans and toffee bits by hand until evenly distributed and dough holds together when pressed.

Divide the dough and shape into four logs, each about 2 1/2 inches wide. Wrap tightly in plastic wrap.

Chill logs in the refrigerator for several hours or preferably overnight.

Preheat the oven to 350°F (175°C). Line baking sheets with parchment.

Using a sharp serrated knife, slice logs into 1/4-inch-thick rounds. Place slices about 2 inches apart on prepared sheets.

Bake for 15–18 minutes, until bottom edges are golden brown. Rotate pans once if oven heats unevenly.

Transfer cookies to a wire rack to cool completely.