Whisk the egg whites in a large clean bowl until stiff. Gradually whisk in the sugars, a teaspoonful at a time, until it has all been added. Whisk for a few minutes more until the meringue mixture is thick and glossy.
Using a dessertspoon, take a large scoop of meringue mixture then scoop off the first spoon using a second spoon and drop on to a large baking sheet lined with nonstick baking paper to make an oval-shaped meringue. Continue until all the mixture has been used.
Bake in a preheated oven, 110°C (225°F), Gas Mark ¼, for 1–1¼ hours or until the meringues are firm and may be easily peeled off the paper. Leave to cool still on the paper.
To serve, roughly mash the banana with the lemon juice. Whip the cream until it forms soft swirls then whisk in 2 tablespoons of the toffee fudge sauce. Combine with the mashed banana then use to sandwich the meringues together in pairs and arrange in paper cake cases. Drizzle with the remaining toffee fudge sauce and serve immediately. Unfilled meringues may be stored in an airtight tin for up to 3 days.