Preheat the oven: preheat the oven to 180°C / 350-375°F / Gas Mark 4-5.
Croissants: working one at a time use a sharp knife and cutting board to slice each of the croissants into small (1 inch) pieces then set aside.
Custard: add the cream cheese to a large mixing bowl and use electric beaters to beat. Then add the cream, caster sugar, eggs, cinnamon powder, lemon juice and vanilla. Combine until consistently mixed with no lumps.
Layer: grease the base and sides of a large baking dish with butter. Then transfer the croissant pieces into the dish and spread them out to form a base layer. Next sprinkle the sultanas into the dish and push them for the most part under the croissant pieces.
Combine: pour the custard over the top of the croissant and sultana layers. Then cover the baking dish with aluminum foil.
Oven bake: place the covered baking dish into the oven (middle shelf) and let it cook for 30 minutes. Once the 30 minute are up use oven mitts to remove the baking dish and set it on a heatproof surface. Discard the foil. Then use the microwave (high, approx 30 seconds) to melt the remaining butter in a heatproof jug. Once the butter has melted, use a pastry brush to coat the top pieces of croissants. Then sprinkle the cinnamon sugar over the top. Return the baking dish to the oven uncovered and cook for a further 10-15 minutes.
To serve: remove the baking dish and let the pudding rest for 5 minutes. Then portion into bowls. Top with your favorite extras such as ice cream, cream, custard or fresh fruit.