Preheat oven to 350 degrees and spray donut pan with cooking oil.
In a medium mixing bowl stir together flour, cornstarch, baking powder, baking soda, nutmeg, and sugar.
Add in milk, sour cream, egg, melted butter, and vanilla extract. Stir together until well combined and smooth.
If you don’t have a piping bag, cut the corner of a Ziploc bag, add batter and pipe the dough evenly into the prepared pans, about 2/3 full in each donut ring.
Set in oven and bake for 9-10 minutes, remove from oven and cool on baking rack.
Remove donuts from baking rack once cooled.
Melt dark chocolate melting wafers in the microwave following package directions. Dip the bottom half of the donut into the chocolate, tap off the extra chocolate and set upside down, chocolate side up on cooling rack and let the chocolate harden. Repeat with remaining donuts.
Once chocolate has hardened, make the topping. Melt unwrapped caramels and milk in a medium mixing bowl for 1 minutes, remove from microwave and stir, then place back in microwave for 30 seconds and stir again. Repeat process until caramel is completely melted and smooth, stir in salt and toasted coconut.
Immediately frost the top of each donut and place back on cool rack to let topping harden. Frost all of the donuts, then use remaining chocolate to drizzle, using a zig-zag motion over the donuts, to get the chocolate lines.
Serve immediately or store on counter until ready to serve.
To store leftovers, if you have any and store in a container with lid or Ziploc bag.