Spoon 1 teaspoon of the lemon curd into the base of each of the four 300ml microwave-safe mugs.
Place the butter in large microwave-safe bowl. Microwave on P-70 (see notes) for 30 seconds or until just melted.
Add the ricotta, sugar, lemon rind, eggs and remaining lemon curd to the melted butter. Mix until well combined. Stir in the flour until well combined. Spoon mixture among the prepared mugs. Microwave on 100, turning mugs halfway through, for 4 minutes or until the cake springs back when lightly touched. Set aside for 5 minutes before topping with double cream and extra lemon curd.