Dough: Preheat oven to 350°F. In a mixer, cream butter, shortening, granulated sugar, and powdered sugar until fluffy (2 mins). Add milk, eggs, and vanilla; mix well. Stir in flour, baking soda, cream of tartar, and salt until dough forms.
Shape: Scoop dough (1.5 tbsp scoops) onto baking sheet. Spray the bottom of a flat glass with nonstick spray, dip into the extra sugar, and press each cookie flat to 1/2 inch thick.
Bake: Bake 6-10 minutes until set on edges but soft in middle. Cool completely on rack.
Chocolate Bottom: Melt 1.5 cups chips with 1 tsp coconut oil. Spread a thin layer on the bottom of each cooled cookie. Place chocolate-side down on parchment to set.
Toast Coconut: Spread coconut on a tray. Bake at 350°F for 4-5 minutes, stirring once, until golden. Watch closely!.
Caramel: Melt caramels, milk, and salt in a saucepan over low heat until smooth. Spread caramel over the top of each cookie. Top immediately with toasted coconut.
Drizzle: Melt remaining 1/4 cup chips with oil. Drizzle over the coconut tops. Let set before serving.