bread_sauce = {'onions': 2,
             'onions': 3,
             'bay leaf' : 1,
             'peppercorn' : 4,
             'mace tsp': 1/4,
             'milk' : 800,
             'breadcrumbs': 150,
             'butter' : 30,
             'onions': 1,
             'double cream tbsp' : 2}

#s_dict = {}
def merge(dicti):
    s_dict = {}
    for key, value in dicti.items():
        print(key, value)
        if not key in s_dict:
            s_dict[key] = [value]
            print(s_dict)
        else:
            s_dict[key].append[value]
            print(s_dict)
    return s_dict


b = merge(bread_sauce)