"In my opinion this is a pretty accurate recreation of the delicious butter that they serve with sourdough bread at Spaghetti Warehouse®. I was having a hard time finding a recipe for this (rather than for the spaghetti) so hopefully this will help someone else!"
Mix butter and garlic together in the bowl of a stand mixer. Beat milk into butter mixture using the whisk attachment on the mixer until smooth and whipped. Add Romano cheese and parsley to butter mixture and beat until thoroughly whipped.
The flavor develops if you let it sit for a little while before serving.
To roast garlic: cut the top 1/2 inch off of a head of garlic and place it in a pan. Drizzle the exposed tops with olive oil, then cover with aluminum foil and bake in an oven at 350 degrees F (177 degrees C) for approximately 40 minutes. The garlic should be easily mashed with a fork. Use a sharp paring knife to remove cloves from the skins.
You can use a food processor to blend butter and garlic if you wish to make it smooth.