Makes 18 squares
225g/8oz/1 cup butter, softened, plus extra to grease
225g/8oz/1 cup caster (superfine) sugar
4 medium (US large) eggs
275g/10oz/2¾ cups self-raising (self-rising) flour, sifted
1 tsp baking powder
grated zest and juice of 1 orange
50g/2oz/½ cup ground almonds
2–3 tbsp milk to mix
18 plums, halved and stoned
50g/2oz/½ cup walnut halves
icing (confectioner’s) sugar to dust
1 Preheat the oven to 180°C/350°F/Gas 4. Butter a 30 × 20cm/12 × 8in shallow tin and line the base with parchment paper.
2 Beat the butter and caster sugar until light and fluffy, then beat in the eggs, one at a time. Fold in the flour, baking powder, orange zest and juice and ground almonds. Slacken the mixture with a little milk.
3 Spoon the mixture into the prepared tin, level the surface and press the plums, cut-side up, into the mixture, spacing them out evenly. Tuck in the walnuts around the plums.
4 Bake in the oven for 30–40 minutes until well risen and golden brown and a skewer inserted into the middle comes out clean. Set aside to cool in the tin.
5 Dust with icing sugar and cut into squares.