To cook the flour- I recommend doing this in a big batch and storing it for future use. Preheat your oven to 350 degrees, and evenly spread flour over the sheet. Bake for about 10 minutes, cool, and store. I find that this process can make the flour clump up a bit, which means you'll want to sift before using it.
In a medium bowl, beat together the butter, sugar, salt, vanilla, and milk until smooth. Sift in the cooked flour (it will likely clump from baking, so sifted is needed here) and beat until smooth. Add a little more flour or milk if you'd like a different consistency.
You can enjoy this now at room temperature, or cold, which is my favorite. Store in a container in the fridge- it will stay good for about a week. Enjoy!