The overlapping mushroom slices make for a gorgeous presentation. The easiest way to create this is with a mandolin because you want the mushrooms sliced very thinly. Hold each mushroom by the stem and use the mandolin to cut very thin slices off the top of the mushroom cap – stop before you reach the stem. You can save the stem ends (they will still have some of the cap attached) for soup or making stock. If you don’t have a mandolin, you can use a large, sharp knife. Remove the stems from the mushrooms. Lay each cap flat on the cutting board and trim one edge, slicing off ⅛ inch or so. Turn the cap on its edge so that the cut side is flush against the board – this way the mushroom remains steady. Slice the mushrooms as thinly as you can. Arrange them on two plates in overlapping concentric circles. Season with salt and pepper. Tear the basil and scatter over the mushrooms. Just before serving, finish each plate with a generous squeeze of lemon and a drizzle of olive oil.