In the bowl of a stand mixer fitted with the paddle attachment, gently blend
the butter, sugars, salt, and vanilla on low speed until light and fluffy, about 5 minutes.
Add the eggs
one at a time, scraping down the bowl after each addition.
the flour, baking soda
, baking powder, and cinnamon together into a large bowl. Add to the creamed mixture all at once and mix on low just until combined.
Stir in the oats, coconut
, raisins, and walnuts by hand. Chill the dough until firm, at least 30 minutes.
While the dough is firming up, preheat the oven to 350 degrees F. Line two baking sheets with parchment paper.
Scoop the dough
onto the prepared baking sheets using a #40 scoop about 1 1/2 inches apart.
Bake until golden brown, 12 to 15 minutes. Rotate and switch the baking sheets as necessary for even baking.
Allow the cookies to cool for a minute on the baking sheets then transfer, using a spatula, to a cooling rack
and allow to cool completely.
Use an offset spatula
to spread a few tablespoons of frosting on half of the cooled cookies, then sandwich the cookies together.
Store the cookies in a single layer in an airtight container.