Step 1

Preheat oven 170°C. Grease ten 5cm metal ring moulds and line with baking paper, ensuring paper is twice as high as the moulds (cakes will rise quite a lot). Beat butter, sugar and lemon rind in an electric mixer fitted with the paddle attachment on low speed until smooth, being careful not to aerate mixture (2-3 minutes). Mix almond meal, polenta and baking powder in a bowl, then beat 2 tbsp polenta mixture into butter mixture. Add eggs one at a time, beating to incorporate between additions, then fold in remaining polenta mixture. Transfer batter to a piping bag fitted with a wide, plain nozzle and pipe into moulds to just below the lip. Bake until golden, well risen and firm to touch (18-20 minutes).

Step 2

For lemon syrup, bring lemon juice and sugar to the boil in a small saucepan, stirring to dissolve sugar. Cool briefly. Poke holes in cakes with a skewer, then pour warm syrup over them (make sure the syrup isn't hot or the cakes will break down). Soak cakes until ready to serve.

Step 3

For mascarpone frosting, whisk ingredients in a bowl to firm peaks (1-2 minutes). Refrigerate until required.

Step 4

For candied pistachio nuts, preheat oven to 150°C. Soak nuts in sugar syrup in a bowl (5 minutes). Drain, then spread nuts over a tray lined with baking paper and bake until golden and crunchy (15-20 minutes; the oil in the nuts means that while warm they're soft, so cool a couple to test for crunch). Cool completely, then coarsely chop.

Step 5

Remove paper from cakes, pipe mascarpone frosting generously on top and serve scattered with chopped candied pistachio nuts. Cakes are best eaten the day they're made.