Preheat the oven to 180°C (360°F) and line a 23cm (9-inch) cake tin with parchment paper.

Wash and cut the rhubarb into small pieces, toss with orange zest, juice, rose water, and cane sugar, then roast in the oven for about 10 minutes.

Cream together the unsalted butter and cane sugar until light and fluffy, then add the orange zest, eggs, and egg whites.

Fold in the ground almonds, plain flour, and baking powder until combined.

Pour half the batter into the prepared tin, layer half the roasted rhubarb, then cover with remaining batter and top with the rest of the rhubarb and slivered almonds.

Bake for 40-50 minutes, or until a knife inserted comes out clean.

Cool in the tin for 10 minutes before transferring to a wire rack.