1. Cut the peppers into quarters, remove all the seeds and white parts, then slice into thin strips.
2. Peel and slice the onions.
3. In a saucepan, sauté the onions with the butter until they are translucent.
4. Then add the pepper strips, olive oil, and thyme sprig.
5. Cook for about ten minutes.
6. After this time, remove the thyme sprig and add the spoonful of sugar, pepper, and salt; let it cook for another 5 minutes.
7. Mix everything well and blend to obtain a smooth and creamy soup.
8. Enjoy warm (or cold in the summer!)