Preheat the oven to 170C/325F/Gas 3 and grease a 1.4 litre/2½ pint shallow ovenproof dish (one that will fit into a roasting tin) with butter.
For the base, very gently warm the milk in a small saucepan. Add the butter, lemon zest and the 50g/2oz of sugar, stir until dissolved.
Lightly whisk the egg yolks in a bowl. Slowly pour the warm milk into the eggs, while whisking.
Sprinkle the breadcrumbs over the base of the buttered dish and pour over the custard. Leave to stand for about 15 minutes, so the breadcrumbs absorb the liquid.
Carefully transfer the dish to a roasting tin and fill the tin halfway with hot water. Bake the custard in the preheated oven for about 25-30 minutes until the custard has set. Remove from the oven and set aside to cool a little.
Meanwhile, put the mixed summer fruits into a pan and warm over a gentle heat. Once they’ve softened and released their juice, add the sugar and cook for a further three minutes.
Heat gently until you have a jam-like consistency. If you are using frozen berries they will release more liquid so you might need to cook for longer to thicken to the right jam consistency.
Whisk the egg whites using an electric hand whisk on full speed until stiff peaks form when the whisk is removed. Add the remaining 175g/6oz sugar a teaspoon at a time, still whisking on maximum speed until the mixture is stiff and shiny. Transfer the meringue mixture to a piping bag.
Spread 4-5 tablespoons of the fruit jam over the set custard, then pipe the meringue on top.
Lower the oven temperature to 150C/300F/Gas 2 and return the pudding to the oven (not in the roasting tin with water) for about 25-30 minutes until the meringue is pale golden all over and crisp. Serve at once with pouring cream.