In a medium saucepan, over moderate heat, bring the broth to a simmer. Cover and keep warm over low heat.
In a risotto pan over medium-low heat, melt 2 tablespoons of the butter with the olive oil. Add rice and stir until it is translucent at edges but still opaque in center, about 3 minutes. Add the garlic and stir for one minute. Add wine and simmer, stirring often, until almost all liquid is absorbed, about 1 minute.
Continue in this way, adding broth 1 cup at a time, and stirring often, until the rice is half cooked, about 8 minutes. Be sure to allow each cup of liquid to be absorbed before adding the next. Stir in the lemon zest and the asparagus. Continue adding broth by cupful's and stirring until rice is almost tender, about 10 minutes longer.
Cook until rice is tender but still firm to bite and the mixture is creamy. Remove from heat. Add the cheese and the remaining 2 tablespoons butter. Stir until cheese and butter melt. Season to taste with salt and pepper. Serve; pass the additional cheese at the table.
To roast asparagus, preheat oven to 425 F. Toss asparagus with 2 tablespoons olive oil and place on baking sheet. Roast in oven for 10 minutes, or until asparagus begins to darken. Remove from oven and sprinkle with sea salt.