Preheat oven to 350 °F
Under cold running water scrub the clams and the mussels and remove the beard. Check that clams and mussels are closed (discard open ones).
In a shallow pot with a lid, heat olive oil over medium high heat, add the sausage and break into small pieces. Cook until browned and cooked all the way through.
Add shallots, fennel and garlic, cook until softened and garlic is just about to brown, about 3 minutes.
Add in the clams and mussels, cook stirring for about 1 minute, pour in the white wine and bring to a boil.
Cover with lid and carefully shake the pot back and forth. Cook until mussels and clams open approximately 5 minutes.
Remove clams and mussels from pot and divide evenly amongst four bowls.
Let sauce simmer for another five minutes so flavour can intensify. Stir in two tablespoons cold butter and parsley swirling pot so the sauce doesn’t split.
While sauce is reducing slice buns and broil in oven until golden brown approx. 2 minutes. Top toasted buns with olive oil and finely chopped garlic.
When ready to serve pour sauce evenly between the bowls making sure to not pour the last bit of sauce because it might be a little sandy from the clams and mussels.
Garnish with green onions, fennel fronds and lemon slices. Serve with toasted buns and enjoy.