In the bowl of an electric mixer fitted with the paddle attachment, cream ½ cup (113 g) softened butter, ¾ cup (199 g) peanut butter, ¾ cup (150 g) packed brown sugar, and ¼ cup (50 g) granulated sugar on medium speed for 2–3 minutes, scraping down the bowl as needed, until light and fluffy.

Add 1 large egg, 1 teaspoon vanilla, 1 tablespoon milk, and ¼ teaspoon salt; mix on low-medium speed just until combined.

Add ½ teaspoon baking soda and 1 ½ cups flour to the bowl. Mix on low speed until the dough just comes together; do not overmix.

Stir in 1 cup toffee chips, 1 cup slightly crushed pretzel twists, and 1 cup Reese’s Pieces with a spatula until evenly distributed.

Line cookie sheets with parchment paper or a Silpat baking mat.

Using a 2-tablespoon scoop or spoon, portion dough into 2-tablespoon balls and place them on the prepared cookie sheets, spacing them about 2 inches apart. Chill the scooped dough on the sheets for at least 30 minutes.

After chilling, preheat the oven to 350°F (175°C).

Bake chilled cookies for 8–10 minutes, until the edges just begin to brown and the centers look set.

Let the cookies cool on the baking sheets for about 5 minutes, then transfer them to a wire rack to cool completely.

Store cooled cookies in an airtight container for up to 3 days, or freeze for up to 3 months.