Set the clams in a colander and rinse and scrub well with a clean brush.
Heat a large skillet over medium high heat with butter and olive oil. Add the garlic and saute 30 seconds. Add the diced tomatoes, if using, the white wine and the clam juice. Simmer on medium low for 12-15 minutes, reducing the liquid.
At this point, the sauce can sit until you are just 15 minutes from serving the clams.
To continue, bring your sauce to a boil. Add the clams and give a quick stir. Cover with a lid and continue to cook on medium high until they all open, 6-9 minutes. Note: You want to cook these quickly to keep them from getting tough. Make sure your liquid is boiling before adding the clams. The clams will cool the liquid down. If any clams don't open, remove from skillet and toss out. Squeeze the lemon juice over the top. Gently move the clams and broth into a large shallow bowl to serve. Top with reserved 1 1/2 tablespoons of butter and reserved 1 tablespoon of minced parsley. Garnish with lemon quarters. Serve while very hot with lots of bread (Italian bread and gluten free) to soak up the broth.