Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, cream together the sugar, brown sugar, shortening, and peanut butter until smooth and fluffy.

Add the salt, vanilla extract, eggs, and milk, mixing until fully combined.

In a separate bowl, whisk together the all-purpose flour and baking soda.

Gradually add the dry ingredients to the wet mixture, stirring until a soft dough forms.

Scoop tablespoon-sized portions of dough and roll them into balls.

Place the cookie dough balls on the prepared baking sheet, leaving space between each one.

Flatten slightly with the back of a spoon or fork.

Bake for 10-12 minutes, or until the edges are lightly golden.

Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

To make the buttercream frosting, beat the unsalted butter in a bowl until creamy.

Gradually add the powdered sugar, mixing on low speed.

Pour in the milk and vanilla extract, then beat until light and fluffy.

If desired, add food coloring for a fun, festive touch.

Once the cookies have cooled, spread or pipe the buttercream frosting onto each one.

Decorate with peanut butter M&Ms for added crunch and color.

Serve and enjoy these rich, nutty, and sweet peanut butter cookies!