Preheat the oven to 375F. Rub the teaspoon of olive oil over the exposed garlic cloves. Wrap the whole head of garlic in foil and place on a baking sheet. Roast for 35-40 minutes, or until the head of garlic is very soft and the cloves are lightly golden.
Place the tahini, water, lemon, mustard, salt, and pepper in a blender or food processor. Squeeze all of the cloves of garlic from the roasted head into the blender. Blend the ingredients on high till creamy and smooth.
Place the beans, celery, shallot, and herbs in a mixing bowl. Add about three quarters of the dressing (you may want to hold off on using all of it until you mix up the salad and see whether you'd like to use more). Use a potato masher or fork to mash the dressing up with the beans and to smash about half of the white beans (you want about half of them to stay intact, or adjust the texture to your liking).
Taste the salad, add more dressing as needed, and season to taste with freshly ground black pepper, additional salt, and/or additional freshly squeezed lemon juice.
Spread the salad on toast and add any optional toppings you like, or serve it as desired.