Apple and date cake

• 125 g unsalted butter, softened, plus extra for greasing
• 120 g pitted dates
• 2 Granny Smith apples, peeled, cored and cut into pieces (1 cm)
• 1 tsp bicarbonate of soda
• 220 g boiling water
• 125 g caster sugar
• 250 g plain flour
• 1 egg
• 1 tsp natural vanilla extract

Almond topping

• 60 g unsalted butter
• 60 g brown sugar
• 2 tbsp milk
• 50 g slivered almonds
• custard, ice cream or whipped cream, for serving