Preheat the oven to 180C/350F/Gas 4.
Line a 30cm/9in deep cake tin with baking parchment.
Heat a frying pan until hot then add the oil and lemon slices.
Fry for 1-2 minutes until just caramelised.
Remove and place caramelised side down in a pattern on the baking parchment in the tin.
Place the butter and sugar into a large bowl and whisk together until light and fluffy.
Add the eggs one at a time, mixing well.
Fold in the ground almonds, polenta, lemon juice and zest and stir to combine.
Pour the mixture over the lemon slices and spread evenly into the tin.
Place in the oven for 25-30 minutes until just risen and golden.
Allow to cool before turning out onto a plate, lemon slices uppermost.
To make the lemon cream, place the mascarpone into a bowl and beat to soften.
Pour in the double cream, lemon vodka, icing sugar and lemon juice.
Whisk until mixture forms soft peaks.
Serve a wedge of cake with a dollop of cream, a sprig of mint and sprinkle of lemon zest.