Preheat the oven to 180°C. Combine the oats and walnuts on a baking tray and bake for about 7 minutes or until the oats are toasted. Allow to cool.
Transfer the oats and walnuts to a food processor and add the cornflakes and sugar. Process to fine crumbs. Add the egg whites and 1 tablespoon of the lime juice, then pulse until evenly moistened.
Line a large baking tray with baking paper. Divide the dough into six pieces. With moistened hands, pat each piece out to a 10-cm round on the paper. Give each round a raised edge. Bake for about 10 minutes or until crisp. Cool for 2 minutes on the baking tray, then transfer the pastry rounds to a wire rack to cool completely.
Combine the remaining 1 tablespoon lime juice with the lime zest and prune purée in a small bowl. Spread the mixture inside the cooled tartlet cases.
Arrange the plums over the prune filling and garnish with lime zest. (The tartlets can be made the day before and kept in the fridge, loosely covered.)
Some more ideas…
• Use pecans or almonds, or a mixture of the two, in place of the walnuts. • Instead of plums, use fresh peaches. Choose peaches that are ripe but firm. There is no need to peel them. • If the tartlets are made the day before you serve them, they will soften enough to be eaten with a knife and fork. •To keep the fresh plums from browning, you can blanch the slices in boiling water for thirty seconds. Cool and garnish as directed. Alternatively, glaze the tartlets with ¼ cup plum jam thinned with about 2 tablespoons of boiling water.
Plums and prunes are rich in potassium and soluble fibre, both key nutrients for battling high blood pressure. They also contain phytochemicals, such as chlorogenic acid, which are thought to detoxify carcinogenic chemicals that enter your body from the environment, such as smoke.