Preheat the oven to 350°F (175°C).

In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth.

Beat in the eggs one at a time, then stir in the vanilla extract.

In another bowl, whisk together the flour, baking soda, and salt.

Gradually blend the dry ingredients into the wet mixture.

Fold in the blue chocolate chips.

Drop rounded tablespoons of dough onto a baking sheet lined with parchment paper.

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

Remove from the oven and let cool on the baking sheet for a few minutes before transferring to a wire rack.

In a small bowl, mix together the powdered sugar, softened butter, milk, and blue food coloring until smooth.

Once the cookies are completely cool, spread the blue frosting on top of each cookie.