Preheat your oven to 140°C (fan) / 160°C. Lightly grease a 1.8-litre ovenproof dish, roughly 25-30cm x 15-20cm.
Butter one side of each slice of gluten-free bread, then cut each slice into triangles.
Add the double cream, milk and vanilla extract to a medium saucepan. Place over a medium-low heat until hot and steaming, but don't allow it to boil.
Meanwhile, add the egg yolks and caster sugar to a large mixing bowl and whisk until well combined.
Gradually pour in the hot cream mixture whilst constantly whisking until smooth and well combined.
Arrange a layer of buttered bread in the base of your prepared dish.
For the classic version, scatter over some of the raisins and sultanas. Add another layer of bread and the remaining dried fruit, then finish with a final layer of bread. Keep the top free from dried fruit so it doesn't burn.
For the triple chocolate version, add the milk, dark and white chocolate chips to a small bowl and mix together. Scatter 100g of the mixed chocolate chips between the layers of bread, keeping them tucked beneath the top layer. Reserve the remaining 20g for later.
For the raspberry and white chocolate version, scatter the raspberries and 60g of the white chocolate chips between the layers of bread. Keep the chocolate tucked beneath the top layer and reserve the remaining 15g for later.
Slowly pour the warm custard evenly over the bread, then gently press the bread down into the custard. Allow to soak for 20-30 minutes, gently pressing the bread down again halfway through if needed.
Place into the preheated oven for 35-40 minutes. The exposed bread on top should be a pale golden colour and lightly crisp around the edges. Don't keep baking until the top is deeply golden or the custard underneath can become firm and grainy instead of remaining lovely and creamy.
Remove from the oven and switch your oven to a medium-high grill. Whilst the grill heats up, generously sprinkle an even layer of caster sugar all over the top.
Once the grill is hot, place the pudding onto an upper shelf for 2-3 minutes until the sugar has melted and the top is golden and caramelised. Keep a close eye on it as it can colour quickly.
For the triple chocolate version, scatter the reserved 20g of mixed chocolate chips over the top as soon as the pudding comes out from under the grill. The heat from the pudding will soften them slightly.
For the raspberry and white chocolate version, scatter the reserved 15g of white chocolate chips over the top as soon as the pudding comes out from under the grill. Again, the warmth from the pudding will soften them slightly.
Allow to stand for 5-10 minutes before serving warm. Sift over the icing sugar, if using. Enjoy!