Melt butter in a pot on the stove top over medium heat.
1 tablespoon butter
Add flour. Quickly whisk the flour and butter together to form a paste, and cook this for a few seconds while stirring.
1 tablespoon all-purpose flour
Combine milk and chicken stock, and pour a splash of the liquid into the pot. Whisk until the liquid is incorporated into the flour paste, then add a little more. Continue to gradually add liquid until the sauce has an even, smooth consistency.
½ cup chicken stock, ½ cup milk
Add very finely diced garlic, apple cider vinegar and seasoning to the sauce, and keep whisking. The sauce will gradually thicken. Add additional seasoning, and lemon juice to taste. I like to squeeze half a lemon at a time, and then check to see if more is needed. Serve the sauce immediately.
3 garlic cloves, 3 lemons, ¼ teaspoon salt, ¼ teaspoon pepper, ½ teaspoon apple cider vinegar, ½ teaspoon dried parsley