How to bake Colm O'Gorman's roasted rhubarb and orange spoon cake

Colm O'Gorman's Roasted Rhubarb and Orange Spoon Cake
This lovely dessert is a bit of a cross between a cake and a pudding; a simple but delicious sponge batter topped with lots of fruit and baked in a shallow casserole, skillet, or ovenproof dish and served with a big spoon directly from the pan — hence the name. It has a fabulous texture, cookie-like around the edges, moving to a light sponge and then a luscious, moist, fruit-laden centre. It is heavenly.
Rhubarb is now fully in season and locally grown is widely available. I adore rhubarb, most particularly when it is simply roasted with the zest and juice of an orange, some star anise and a little honey. My roasted rhubarb is fabulous served over creamy yoghurt or with pancakes for breakfast and it is divine with this cake. I part-roast the rhubarb when using it for this recipe as it will finish cooking when the cake is baking in the oven. I always roast more rhubarb than I need for the top of the cake and use the extra fruit when serving the dessert or for breakfast the next day.