Over a hot grill or an open gas-stove flame, char the corn until well blackened but not completely burnt. Remove from heat, and when cool enough to handle, shave off kernels using a chef’s knife and reserve.
Heat a large sauté pan over medium heat. Melt the butter, then add fennel and garlic. Sweat for 2 minutes, then turn up the heat a bit and sauté until just cooked through, about five to seven minutes. Add the epazote and the charred kernels of corn to the mixture, and toss to combine until heated through.
Remove from heat. Stir in cotija, olive oil, and chipotle powder. Squeeze the lime into the mixture. Season with salt.