Clean and wash the beans, cook them in salted boiling water for 8-10 minutes, they should still have bite, but no longer be raw. Drain well and place in a shallow bowl.
Heat the butter, add the oil, fry the cleaned and sliced spring onions and pour over the beans.
Mix the juice of one lemon with the olive oil and the finely chopped garlic and pour it over the bean and onion mixture. Season with pepper and, if necessary, add salt and sugar. Garnish with lemon wedges.