Wash clams well. Wash mussels, making sure to remove and discard their beards. Heat 1 tablespoon olive oil in each of 2 large cast iron frying pans over high heat. Add clams and half the thyme to 1 of the pans; add mussels and half of the thyme to the other pan; cook for 1 minute. Divide butter and capers between the 2 pans. Continue cooking clams and mussels for 2 to 3 minutes, or until they open.
To serve, place clams mussels and the butter in which they cooked in a warmed serving bowl and sprinkle with fleur de sel. Serve with bread on the side, to soak up the butter at the bottom of the bowl.
If you don't have access to fleur de sel, substitute sea salt.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.