If desired, cut lemons in half crosswise, in a decorative zig-zag pattern. Squeeze the juice, reserving 2 tablespoons.
Using a small paring knife, take out the white pith. Carefully cut off enough from the lower half of each shell to make them stand. Keep refrigerated, covered until the time of usage.
Beat the whipped cream in a chilled bowl with chilled beaters until smooth and fluffy. Add the horseradish, lemon juice leftover, and garlic; season to your taste with salt. Keep refrigerated until ready.
After washing thoroughly, arrange the spinach leaves on 4 chilled salad plates.
Put spoonfuls of the horseradish cream sauce into the lemon hollows. Place one on each dish.
Thread eel fillets onto the skewers; place on spinach leaves. Serve cold.
Serving Suggestions: Serve with thin slices of buttered bread, oatcakes or toast.