Heat oil in a medium frying pan
over medium-high heat. When it shimmers, add shallots, season with salt and freshly ground black pepper, and cook until golden brown, about 2 minutes. Sprinkle flour over the top and cook until raw taste is gone, about 30 seconds. Add stock
and bring to a boil. Stir in lettuce and peas, reduce heat to medium-low, cover, and simmer
until lettuce and peas are tender, about 5 minutes. Stir in yogurt or sour cream
, if using. Taste, adjust seasoning as desired, and serve.