Preheat the oven to 325. Line a standard muffin pan with paper liners.
In a large bowl beat the butter and sugar until fluffy. Add the 3 tablespoons of oil and beat until it's combined.
Add the flour, cornstarch, baking powder, kosher salt, and instant vanilla pudding to the bowl. Beat -- the mixture will form coarse buttery crumbs.
Crack the eggs into a medium bowl and whisk them lightly to break the yolks. Add the remaining ½ cup oil, milk, rum, and vanilla.
Whisk to combine and then add the wet ingredients to the dry. Beat until smooth.
Portion the batter into the prepared muffin cups. I use a ¼ cup measure and fill them mostly full -- about ¾ of the way.
Bake for 18 - 20 minutes or until a pick inserted into the center comes out clean.
Let the cupcakes cool before frosting.
To make the frosting whip the butter with a whisk attachment. Add the powdered sugar a cup at a time. After 3 cups add the cinnamon and salt. Beat to combine. Add the last 2 cups of frosting and the rum. If you like a thinner frosting add more rum. (**see note**).
To toast the coconut scatter the sweetened flaked across a baking sheet and place it in the preheated oven after you take out the cupcakes. It only needs 3-5 minutes max. Watch it closely and remove it as soon as some of the coconut is golden.
Frost the cupcakes and sprinkle each with a little toasted coconut.
Notes
To pipe the buttercream as shown you'll need a little more than the recipe calls for. Increase the frosting measurements by adding another ½ cup butter, 1½ cups powdered sugar, and another tablespoon or two more of rum (to your desired consistency). You can also increase the cinnamon by adding another ½ teaspoon.
Recipe by Sugar Dish Me at https://www.sugardishme.com/spiced-rum-cupcakes-with-boozy-buttercream/