Sift powdered sugar through a sifter or fine metal mesh sieve to remove lumps and set aside.
Create a double-broiler with a glass mixing bowl that when sitting on top of the saucepan is a few inches from the bottom of the saucepan. Fill the saucepan with a few inches of water (but not enough to touch the glass mixing bowl!).
In the mixing bowl, combine chocolate, oil and milk and melt over low-medium heat. Stir occasionally.
When this mixture is smooth, remove from heat and add the powdered sugar. If there are still any lumps, place bowl back on the saucepan for a few minutes and stir occasionally until the mixture is smooth then remove from heat again.
Stir in salt and vanilla extract.
Let this mixture cool until it thickens but is still spreadable. You can speed this process up by placing the bowl in the fridge for up to 15 minutes.
Use a cookie scoop to place topping on cookies then spread with an offset spatula or transfer to a glass liquid measuring cup to pour over a bundt cake.
After topping cake or cookies, let the glaze set before you enjoy (approximately one hour). Leftovers can be refrigerated in an air-tight container but the glaze will harden when cool so you will need to reheat to make it spreadable again.