Step 1 Cut off the stem top and root bottom from each onion and discard. Cut each onion into 1/4-inch thick slices. Set aside.
Step 2 Trim the stem top and bottom off of each pepper. Cut each pepper in half lengthwise. Scrape out the seeds and discard. Cut each half into 1/4-inch slices crosswise. Set aside.
Step 3Strip the ears of corn off the husk, remove the silk and discard. Holding each ear upright, narrow end at the top, cut the kernels off the cob using a sharp knife.
Step 4Bring a large pot of water to boil and add the corn. Cook until tender, about 3 minutes. Drain and set aside.
Step 5Melt 5 tablespoons of butter in a skillet over medium heat and tilt the pan so the butter covers the bottom. Add the onions and cook, stirring occasionally, until softened but not browned, 8 to 10 minutes. Remove them from the skillet to a serving bowl.
Step 6There should be a little butter in the skillet, but if not, add the remaining tablespoon. Add the pepper strips and cook, stirring, until softened, 12 to 14 minutes. Lift them out of the skillet and add them to the onions. Add the corn to the skillet and cook, stirring, until tender, 3 to 4 minutes. Add the corn to the onions and peppers.
Step 7Add salt to taste and lightly stir so the salt is spread through the vegetables. Add more salt if needed. Serve hot or warm.