Preheat your oven to 350 degrees Fahrenheit, and line a baking sheet with parchment paper. Set aside.
In a medium mixing bowl, whisk together flour, baking soda, baking powder, and salt.
In a large mixing bowl, beat together 1 cup butter and sugar until light and fluffy.
Add egg, egg yolk, and 2 tsp. vanilla, mix well.
Slowly add flour mixture, mixing as you go. If dough becomes too thick, use cookie dough beaters or fold the mixture together until everything is incorporated.
Use a 1.5 inch cookie scoop to scoop the cookies onto the lined baking sheet, about 2 inches apart.
Bake for 9-11 minutes, until edges of cookies are golden brown.
Allow the cookies to cool slightly, then move them to a cooling rack to finish cooling.
For the frosting, beat 1 cup of butter, until smooth.
Mix in salt, and 1 tsp. Vanilla.
Slowly add powdered sugar, mixing to combine.
Divide the frosting mixture in half into two separate bowls.
To the first bowl, add 3-4 drops of blue food coloring. Mix well.
To the second bowl, add 3-4 drops of teal food coloring and mix well.
To combine the frostings together, lay out two pieces of plastic wrap.
Add the blue frosting to one and the teal frosting to the other.
Wrap up the frostings inside the plastic wrap, twisting the ends.
Snip off one of the twisted ends of the wrap.
To a piping bag with a 4B star tip, add both colors, with the end you cut towards the bottom near the piping tip.
Gently squeeze the bag with even pressure so that the colors come out together.
Add frosting to your cookies, and top with a gummy shark.