For the corn broth: Break or chop the corn cobs in two. In a large pot, add the water, salt, garlic, and corn cobs. Bring to a boil, then turn the heat down to the minimum, cover, and simmer for 1 hour.
Discard the garlic cloves. Using tongs, pick up the cobs and scrape kernel bits still clinging to the cobs back into the pot. Don’t strain--you should end up with about 4 cups (1 L) of corn broth. Discard the cobs and keep the broth warm. If you’re making the broth in advance, store it in an airtight container and refrigerate for up to two days.
For the corn risotto: If you refrigerated the corn broth, pour it back into a saucepan. Warm over low heat until just simmering, then keep warm.
In a large, shallow pan, or in a round braiser, warm the olive oil over medium-low heat. Add the shallot and sauté until soft, about 3 minutes. Add the garlic and thyme leaves and cook, stirring, for 1 minute. Add the rice and cook, stirring, for 2 minutes. Add the white wine and simmer until the wine is absorbed. Turn the heat down to low, then add 1 ladleful of corn broth; stir until the broth is almost completely absorbed. Continue adding broth, one ladleful at a time, allowing each ladle to be absorbed before adding more. Risotto is perfectly cooked when it is tender with a little bite—stop adding broth once you reach that stage (you should have a bit of broth remaining.)
Add the butter and Parmigiano-Reggiano and stir vigorously, until melted and incorporated. Stir in the corn kernels and one more ladleful of corn broth. Taste and adjust seasoning, if needed. Remove from the heat, cover, and let sit for 5 minutes.
To serve: Divide the corn risotto between warm shallow bowls. Sprinkle with fresh thyme leaves and some freshly ground black pepper. Serve immediately.
You will have more kernels than you need for the risotto. Throw the remaining kernels into soups, fried rice, stir-fries, or salads, or store them in a large ziplock bag and freeze for later use.
Turn this risotto into a heartier--divine!—meal by top it with grilled shrimp, cooked crab, or lobster meat.