This rich risotto marries the distinctive taste of baby artichokes with creamy mascarpone cheese and sprightly lemon and thyme.
Remove 3 teaspoons grated zest from 1 lemon; halve the lemon, and squeeze out 1 tablespoon juice. Set zest and juice aside. Cut remaining lemon in half, and squeeze into a medium bowl of cold water; add all rinds to water.
Prepare the artichokes: Working with 1 artichoke at a time, snap off tough outer leaves until pale-green leaves are exposed. Cut off top third. Using a paring knife, peel dark-green layer from base and stem; trim stem. Quarter artichoke lengthwise. Transfer to lemon water.
Bring stock and bay leaf to a simmer in a medium saucepan over medium-high heat; reduce heat to low.
Melt butter with oil in a large saute pan over medium heat. Add onion, garlic, and a pinch of salt; cook, stirring occasionally, until onion is slightly softened, about 6 minutes. Drain artichokes, and add to pan. Cook, stirring often, until artichokes are just tender, about 12 minutes. Add rice, and stir until coated, about 1 minute. Pour in wine, and cook, stirring, until wine has almost evaporated, about 3 minutes.
Add enough hot stock (about 1 cup) to just cover rice. Cook, stirring, until stock is almost absorbed. Continue adding stock, 3/4 cup at a time, waiting for each addition to be absorbed before adding the next; cook, stirring, until rice is tender but still slightly firm in the center, 20 to 25 minutes. Remove from heat, and discard bay leaf.
Stir in chopped thyme; season with salt and pepper. Add mascarpone, 2 teaspoons lemon zest, and the lemon juice; stir until mascarpone is melted and rice is moist and creamy. Serve immediately, garnished with thyme sprigs and remaining teaspoon lemon zest.