3 tablespoons butter
½ onion, roughly chopped
½ leek, roughly chopped
small bunch sage, roughly chopped
2 cups vegetable broth
3 tablespoons flour
1 teaspoon lemon juice
sea salt and pepper, to taste
Caramelize onions and leeks in half the butter. Add sage, the rest of the butter, and the flour, stirring until flour is well incorporated. Cook the flour and butter mixture for 2–3 minutes, stirring constantly. Over medium-high heat, gradually add vegetable stock, stirring in each time to maintain a smooth texture. Turn heat to low, cover, and simmer for 15 minutes. Season with lemon juice, salt and pepper. You can adjust the thickness as desired by adding more water or by simmering uncovered.