Plum and pistachio cake

Ingredients

• Topping
• 60 gram unsalted butter
• 1/4 cup (55g) demerara sugar
• 1 teaspoon allspice
• 2 67 g eggs, beaten
• 90 gram unsalted butter, at room temperature, plus extra, to grease
• 90 gram caster sugar
• 1 cup (150g) plain flour
• 1 teaspoon baking powder
• 2 tablespoon milk
• 60 gram chopped pistachio kernels
• 12 red-fleshed plums, halved and deseeded
• thick cream, to serve