This souffle rises only modestly, and doesn't have the dramatic crown of some souffles. It is not temperamental, but if it doesn't puff up, don't tell anyone it was meant to be a souffle. It has an excellent flavour and succeeds as a humble casserole. The molasses gives it a spicy, mildly sweet flavour.

Preheat oven to 200°C (400°F) Gas Mark 6. Grease and flour a 1.2 litre (2 pt) souffle dish, making sure you grease sides all the way to the top.

Puree sweet potatoes in blender or food processor. Grate apple and toss with flour (which will absorb any liquids that run out of apple as it cooks).

Mix apple and sweet potato, then add all remaining ingredients except egg whites and cream of tartar.

In a separate bowl, beat 3 egg whites and cream of tartar until soft peaks form. Gently fold about 1/3 of the egg whites into the sweet potatoes, then fold in the rest.

Stir the mixture as little as possible in order to keep the egg whites airy. Pour the mixture into the souffle dish. Bake at 200°C (400°F/) Gas Mark 6 until top is lightly browned, about 35 minutes.