• Build the custard

  Preheat the oven to 160°C. Gently heat the milk and butter in a saucepan until the butter melts and the milk is warm — do not let it boil. In a separate bowl, whisk together the caster sugar, egg yolks and orange zest until pale, then slowly whisk in the warm milk to make a smooth custard.
  
• Prepare the base

  Remove the crusts from the bread and pulse in a food process or until you have fine breadcrumbs. Divide the breadcrumbs evenly between six ovenproof jars or ramekins (or one large ovenproof dish), then pour the custard over the top.
• Bake and cool

  Place the jars, or large ovenproof dish, in a roasting tin and pour in enough hot water to come halfway up their sides (a bain-marie). Bake for 15 minutes, until just set with a gentle wobble. Remove from the oven and leave to cool completely. Reduce the oven temperature to 150°C.
• Make the jam

  While the custard cools, place the strawberries, raspberries and orange juice in a small saucepan. Warm gently until the fruit softens and releases its juices. Stir in the caster sugar and continue cooking gently for about 3 minutes, stirring occasionally, until the mixture reaches a soft, jam-like consistency. Set aside to cool slightly.
  
• Whip the meringue

  In a clean, grease-free bowl, whisk the egg whites to soft peaks. With the whisk still running, add the caster sugar a spoonful at a time, whisking well between additions, until the meringue is thick, glossy and holds a firm peak.
  
• Assemble and finish

  Spoon the cooled jam evenly over each custard base. Spoon or pipe the meringue on top in generous swirls, covering the jam completely. Bake for a final 15 minutes, until the meringue is golden and lightly crisp on the outside. Serve warm or at room temperature.

Chef's Notes     A bain-marie prevents the custard from curdling or overcooking —don't skip it.   Make sure the mixing bowl and whisk are completely grease-free before whipping the egg whites, or the meringue won't hold peaks.   The jam can be made a day ahead and kept chilled until needed.    For neat swirls, pipe the meringue with a large open star nozzle; for a rustic look, simply spoon and swirl with the back of a spoon.