415 is about 65 degrees too hot, even for the essential. While the essential will tolerate and little extra heat it doesn't meant that the temps should be pushed. Try stopping the cooking at 45 seconds and stir your plastic well. Then start the microwave again for 20 seconds and stop/stir again and check the temp this time. Do 15 second stop/stirs and temp reading from that point on until your plastic just reaches 350. That's all the hotter you should need it to get started.