For the stock:
Place all ingredients in a large pot and bring to a boil. Reduce heat to a lively simmer and cook to reduce liquid to 2 cups, approximately 30 minutes. Strain and reserve, keeping stock warm.
To finish the corn:
Begin heating a large saucepan, and glaze bottom with the extra-virgin olive oil. Add the lardons and cook over medium heat, rendering the fat and browning the pieces, stirring as needed. Add the onion and sweat, about 45 seconds. Add the garlic and continue to cook, stirring, another 30 seconds. Add the corn and salt, continuing to cook for another 2 minutes. Add the reserved corncob stock and bring to a simmer, cooking until the liquid reduces to approximately 2/3 cup. Add the creme fraiche and simmer 3 minutes or until the mixture begins to thicken. Add the butter and stir. Remove pan from heat; stir in cilantro and lime zest. Check for seasoning and serve.