A delicious and different way to use sorrel leaves - sorrel is usually used in soup and omelette recipes. These little herb tarts are so summery and make wonderful picnic food, as well as interesting appetisers. I have wild, woodland and cultivated sorrel in my garden, but prefer the tangy almost lemon and vinegar taste of wild sorrel leaves in these little tarts. Serve these warm or at room temperature with lightly dressed salad leaves and a glass of crisp, chilled Chablis or Chardonnay. Notes on using sorrel leaves: Sorrel is one of those ingredients that feature all too rarely in our kitchens, yet its bite and acidity make it one of summer's top temptations. When you're cooking the larger, mature leaves, strip out and discard the stalks, just as you would with spinach, before cooking. Avoid aluminium or cast-iron pans, though, because the oxalic acid in the leaves reacts with the metal and affects the flavour.