Literally: don’t go with the back of the spoon
Meaning: Analogy to real life, meaning to do something without hesitation, without restriction. To go for it!
Origins: 19th, 20th century, Proust used it in his novel À la recherche du temps perdu. It would be very tough to use the back of the spoon to eat, for example soup or yogurt. Contrary to the one using the spoon the normal way can enjoy a dish.
Nowadays, this expression is less used than those expression “ne pas aller de main morte” or "ne pas mâcher ses mots"