Light a grill or preheat a grill pan. Grill the tomatillos and corn over a moderately hot fire or moderate heat until lightly charred all over, about 4 minutes per side. Transfer to a plate. Grill the onion slices until lightly charred, about 3 minutes per side. Remove the charred skins from the tomatillos and quarter them. Slice the corn kernels off the cob. Cut the onion into 1/4-inch dice.
In a skillet, fry the bacon until crisp. Drain on paper towels and coarsely chop. In a bowl, combine the garlic with the chipotle, then stir in the tomatillos, corn, onion and bacon. Fold in the purple basil, season with salt and pepper and serve.