Salade D’haricots Vert (French Green Beans)

INGREDIENTS 500g/1lbs French beans (Haricots Vert) 40 g/ 2 Tbs unsalted butter 100 g yellow onion finely sliced (or one small onion) 3  fresh ripe tomatoes/1 cup  medium diced 2 garlic cloves minced 200 ml/1 cup vegetables stock 1 Tbs “Cote d’Azur”...