La recette literally translates to "the recipe". It's an interesting phrase in this song because it's used metaphorically.
In the context of the lyrics, "La recette, c'est toi et moi" (The recipe, it's you and me) implies that the 'recipe' for their relationship, for happiness, or for overcoming challenges, is simply their togetherness. It's a sweet and unique way to express the essential role of their bond.
Have you ever felt like your relationship was the perfect recipe for happiness, but your partner was about to throw it all away? That's the feeling at the heart of Slimane's song "La Recette." He's talking to a lover who seems ready to leave, and he's completely baffled. He keeps repeating the central idea: "La recette, c'est toi et moi" [The recipe, it's you and me]. For him, their combination is the only one that works.
This isn't a perfect, fairytale romance. Slimane admits there's serious conflict, singing, "Ça crie, ça casse tout dans la maison" [There's screaming, everything's breaking in the house]. But despite the fighting, he can't imagine life without this person. He pleads with them, asking for clear reasons for their doubts: "posons les cartes sur la table / Donne-moi des raisons valables" [let's put the cards on the table / Give me valid reasons]. The song builds into a desperate and obsessive loop of him begging, "Ne me quitte pas" [Don't leave me], because in his head, there is only them.