Adapted from https://food52.com/recipes/5108-buttermilk-bagna-cauda
Drop the garlic and thyme into a small saucepan, add the butter and melt over low heat. Simmer the garlic (pulling the pan off the heat if the butter ever bubbles actively) until it's softened, about 10 minutes.
Add the anchovies and mash with a wooden spoon to dissolve them. Stir in the olive oil and let heat through. Season with salt -- taste as you go! (LB addition—I also stir in extra olive oil and spicy pepper flakes)
Whisk in the buttermilk. Serve with a platter of vegetables. Kalamata olive bread is also traditionally served with this dish.