Step 1

Cover whole mandarins in medium saucepan with cold water; bring to a boil. Drain then repeat process two more times. Cool mandarins to room temperature.

Step 2

Preheat oven to moderately slow, 170°C (150°C fan-forced). Grease deep 22cm-round cake pan; line base with baking paper.

Step 3

Blend or process nuts until mixture forms a coarse meal. Halve mandarins; discard seeds. Blend or process mandarins until pulpy.

Step 4

Beat butter, extract and caster sugar in small bowl with electric mixer until light and fluffy. Add eggs, one at a time, beating until just combined between additions; transfer to large bowl. Stir in polenta, baking powder, nut meal and mandarin pulp.

Step 5

Spread mixture into pan; bake about 1 hour. Stand cake 15 minutes; turn, top-side up, onto wire rack to cool. Serve cake dusted with sifted icing sugar.