Pre-heat oven to 200C/400F/Gas mark 6. Place a cast iron frying pan, skillet or heavy based baking dish into the oven to pre-heat.
Whisk the eggs with the sugar until light and frothy. The add the milk, flour, vanilla extract and salt, and whisk again until you have a smooth lump-free batter. (At this stage you can cover the batter and leave it overnight or for a few hours until you need it).
Open the oven and using a heavy duty oven glove, take the heated pan out of the oven and add the butter, swirling it around to coat the pan until it is all melted. Then pour the batter into the pan and place it back into the oven immediately.
Bake for 20 to 25 minutes until it is puffed up and golden brown, the edges will have shrunk away from the pan too.
Spoon the rhubarb and strawberry conserve over the top, then sprinkle some of the crumble topping over as well as a dusting of icing sugar. Serve straight away cut into wedges and with extra conserve, crumble topping and icing sugar on the side.