Whisk the egg whites and cream of tartar in a large clean bowl until stiff. Combine the sugars then gradually whisk into the egg white, a little at a time, until it has all been added. Whisk for a few minutes more until the meringue mixture is thick and glossy. Fold in the walnuts.
Divide the meringue mixture evenly between 2 greased 20 cm (8 inch) sandwich tins, base-lined with nonstick baking paper. Spread the surfaces level then swirl the tops with the back of a spoon. Bake in a preheated oven, 150°C (300°F), Gas Mark 2, for 35–45 minutes until lightly browned and crisp. Loosen the edges and leave to cool in the tins.
Re-loosen the edges of the meringues and turn out on to 2 clean tea towels. Peel off the lining paper then put one of the meringues on a serving plate.
Whip the cream until softly peaking then spoon three-quarters over the meringue. Halve 8 of the smallest strawberries and set aside. Hull and slice the rest and arrange on the cream. Cover with the second meringue, top uppermost. Decorate with spoonfuls of the remaining cream and the reserved halved strawberries. Serve within 2 hours of assembly.