My search for a taste of Marseille beyond the Provençal clichés—homes of the elderly Le Panier district—had taken an unexpected turn. A turn into the kitchen of Agnès Daragon, a Harley-driving nurse who teaches country dancing.

Which well captures the bold strokes with which she cooks. From a stockpot simmering in her dark wood-and-ochre kitchen on the outskirts of the city, she ladles bowls of brothy beans and vegetables. Into each bowl, she spoons a mound of a luminous green paste that looks like pesto, but Daragon calls by the French pistou.

I tint the broth green as I stir in the paste and immediately am awash in waves of peppery basil, savory Parmesan, unctuous olive oil, sweet tomato. Each bite is rich with vegetables swaddled in herb and garlic. The soup—literally soupe au pistou—is light and fresh, yet deeply savory.

As Daragon walks me through the recipe, it’s obvious the pistou is the key. The soup is lovely—dried beans simmered tender; tomatoes; carrots; green beans and zucchini sweetening the water into broth; pasta tossed in to thicken it—but it is the pistou that elevates, unifies it all.

To make it, she fills a stone mortar with pine nuts, basil, clove upon clove of garlic, Parmesan and olive oil, then mashes it all. The ingredients are the same, but this is nothing like the pesto of Genoa, Italy, the latter a study in order and balance—and with far less garlic—each ingredient added in its own time.

By comparison, pistou is a rollicking, bashing affair of overwhelming garlic, everything dumped in at once, pounded to a pungent mash. I taste it and it’s so strong my tongue stings. Of course. Unlike Italian pesto—which is barely thinned when tossed with pasta—pistou is diluted, suffusing the broth and mixing with the sweet vegetables.

Back at Milk Street, soupe au pistou adapted easily to our kitchen. We mostly followed Daragon’s recipe, adding leeks and garlic to the beans to reinforce the flavors of the vegetables and pistou. We also staggered the vegetables, adding some later in the cooking to preserve their textures. Finally, we opted for the ease of making the pistou in the food processor.

My only regret—failing to snag a ride on the back of Daragon’s Harley.