At La Perla, these mussels are drizzled with additional garlic butter. 
For an elegant presentation, serve them nestled on a platter of rock salt.

Ingredients
12 oz (360 g) fresh spinach, washed and stemmed

2 lb (1 kg) fresh mussels, scrubbed and debearded

2 tbsp (30 mL) garlic butter

1/2 cup (125 mL) onion, finely chopped

1/2 cup (125 mL) ricotta cheese

salt and pepper to taste

3 oz (100 g) provolone cheese, grated

Directions
Blanch spinach for 30 seconds. Cool, squeeze out excess moisture and chop. Reserve.

Steam prepared mussels in 1/4 cup (60 mL) water until shells open, about 5 minutes. Discard any that do not open. Refresh in cold water and remove half the shell so you are left with a mussel on the half-shell.

Preheat oven broiler. In a medium-sized skillet, melt garlic butter and sauté onion until translucent. Add spinach and cook for 2 minutes. Stir in ricotta, salt and pepper. Remove from heat, cool and add provolone. Arrange mussels on a large baking tray. Top mussels with spinach mixture and place under broiler until hot. Drizzle with additional melted garlic butter, if desired. Serves 4.