Before cooking, soak clams for 20 minutes in a pot of cold, salted water. The salt will help draw the sand out of the clams.
In a large pot, combine clams, chicken stock, garlic, onion, butter, 1 Tbs. parsley, lemon juice, thyme, sea salt, and red pepper flakes.
Bring pot to a boil over med-high heat, cover and cook until clams have opened. About 3-5 minutes.
Pour clams and broth into large bowl and garnish with remaining parsley and any extra lemon.