Soak the white beans overnight in a bowl with just enough cold water to cover them.
The next day, drain the water from the beans and rinse well. Cook in boiling water for 45 to 60 minutes. Reserve.
In large saucepan, melt butter in oil over medium heat. Add the onions and cook for 2 minutes until golden brown.
Add carrots and celery. Season and cook for another 2 minutes.
Add the potatoes and stir. Continue cooking for 2 minutes.
Stir in spinach and continue cooking for 2 minutes.
Add vegetable stock, crushed tomatoes, and thyme sprigs. Season. Put a lid on the pan and cook the soup over low heat for about 2 hours, stirring occasionally. It’s important that the minestrone soup simmer gently.
After 2 hours of cooking, add cooked beans and pasta and continue cooking for 20 minutes. Check the seasoning.