01 - Preheat oven to 350°F. Grease an 8x8-inch baking dish with butter.
02 - Place cinnamon roll bread cubes evenly in the dish, layering raisins or sultanas between if using.
03 - Whisk together eggs, granulated sugar, vanilla extract, cinnamon, nutmeg, and salt until fully combined.
04 - Add whole milk and heavy cream to the egg mixture and whisk until smooth.
05 - Pour custard evenly over the bread cubes, gently pressing to ensure full absorption. Let rest for 10 minutes.
06 - Dot the surface with softened butter and sprinkle demerara sugar if desired.
07 - Bake for 35 to 40 minutes until custard is set and top is golden brown.
08 - Remove from oven, allow to cool slightly, then dust with powdered sugar before serving warm.