Cream together the butter and sugars. To that add the vanilla, salt, and egg yolk. Add flour one cup at a time until completely incorporated. Then, BY HAND or on low speed w/ mixer, fold in the mini chips.
While you wait for the oven to warm, wrap your dough in plastic wrap and chill for at least thirty minutes. When it is chilled, roll out cookies on lightly floured parchment and bake at 350° for 8-10 minutes. (I rolled mine like 1/2" thick)
Frost cooled cookies however desired. For the purple heart cookies pictured above I used Royal Icing (this particular recipe.)