Whether you froze it yourself or bought it at the supermarket, the rules for cooking frozen corn on the cob are not substantially different from those for cooking fresh corn - it just takes a little longer. We skip the thawing step and proceed directly to cooking. And much to the surprise of one of our outspoken readers, we're going to suggest pressure cooking as the "best" way, although microwaving, baking, and grilling are also fine options.
To cook frozen corn in a pressure cooker (recognizing that not all pressure cookers are created equal), put a cup of water in the pressure cooker, put the trivet or steamer basket that came with the pressure cooker in the bottom, and put the corn on top. Put the pressure cooker over medium-high heat, and wait until it has come up to pressure. Lower the heat to medium and let it cook for 4 to 5 minutes. Release the pressure quickly, open it once the pressure has completely dissipated, and remove the corn.
To cook frozen corn in a microwave oven (recognizing that not all microwave ovens are created equal), either place 1/4 cup of water and the frozen corn in a 2 quart microwavable dish, cover and microwave on high until thoroughly heated (turning the ears over halfway through cooking time), or wrap each ear in a paper towel, dampen them thoroughly, and microwave on high until well heated. Four ears are likely to take 8 to 10 minutes; eight ears will be in the 13 to 15 minute range; and a dozen ears may take 18 to 20 minutes. Because microwave ovens vary, the times are approximate.
To grill frozen corn, preheat the grill. Place each ear of frozen corn on a sheet of heavy duty aluminum foil. Brush butter over the ears, wrap them in the foil, and put the corn on the grill. Grill for 25 to 35 minutes with the grill lid closed, turning occasionally, until thoroughly heated.
To bake frozen corn in the oven, preheat the oven to 425°F (220°C). Rub the ears with a little butter, wrap them in aluminum foil, place them on a rack in the oven and cook for 25 to 35 minutes. Place a jelly-roll pan on a lower rack under the corn to catch any drips.
We do not recommend for frozen corn the most common method of cooking fresh corn - dunking it in boiling water - unless you thaw the corn first. Throwing huge corn-ice-cubes in the boiling water causes it to lose so much heat, it takes forever to bring the water back to a boil and so is just not an effective cooking medium.