Method

• 1.
  Preheat oven to 160°C. Grease base and side of a 25cm springform cake pan. Line base with 1 layer of baking paper and side with 3 layers of baking paper. Place on a baking tray and set aside.

• 2.
  For lemon caramel, heat sugar and extra lemon juice in a large frypan over medium heat and cook, swirling occasionally, until sugar dissolves. Cook, without stirring, until golden caramel (this should take about 6 minutes). Increase heat to high, add sliced lemon and cook for 6-8 minutes or until slices are caramelised. Using a slotted spoon, transfer 6 lemon slices to a plate, then arrange remaining slices over base of prepared pan. Carefully pour over lemon caramel and set aside to cool.
• 3.
  Meanwhile, to make the cake, place butter and sugar in a stand mixer fitted with the paddle attachment and beat until pale. Add eggs, 1 at a time, beating well after each addition, then fold in vanilla. Combine almond meal, polenta and baking powder in a small bowl, then fold into butter mixture. Add rosemary and lemon zest and juice, and stir to combine.
• 4.
  Pour into pan and bake, covering with foil halfway, for 1 hour 45 minutes or until golden and a skewer inserted into the centre comes out clean (cake may have a slight dip in middle; this is fine). Stand in pan for 1 hour to cool, then invert cake onto a plate, remove baking paper and chill for 1 hour or overnight to firm slightly.
• 5.
  Meanwhile, for the lemon curd, place all ingredients in a heatproof bowl set over a saucepan of gently simmering water (don’t let the bowl touch the water) and stir constantly for 8 minutes or until thickened. Strain into a heatproof bowl, cover directly with plastic wrap and chill for 1 hour to cool completely.
• 6.
  Place the sour cream in a bowl and whisk to stiff peaks.
• 7.
  To serve, halve cake horizontally using a large serrated knife and fill with curd and sour cream. Gently warm reserved lemon slices and arrange on top.