Place the clams in a heavy pot, add half the wine, cover, and heat over a high flame just until the clams open. Discard the shells, cut the clams into small pieces, and reserve. Strain the cooking liquid through a sieve line with a paper towel, add to the stock, and simmer in another pot.
Sauté the onion in the butter and oil until translucent. Add the garlic, rice, and half the herbs and continue cooking for several minutes. Add the remaining wine and stir until most has evaporated. Add the stock. a ladleful at a time, stirring continually, until the rice is just tender. Add the reserved clams and heat through. Turn the risotto onto a platter, top with the remaining herbs, and serve immediately.