Preheat the oven to 180°C.
Line a 30cm deep cake tin with baking parchment.
Heat oil in a frying pan and add lemon slices.
Fry slices for 2 minutes until caramelised.
Arrange lemons caramelised side down in the cake tin.
Whisk butter and sugar until light and fluffy.
Add eggs one at a time and mix well.
Fold in almonds, polenta, lemon juice, and zest.
Pour mixture over lemons and spread evenly.
Bake for 30 minutes until risen and golden.
Cool and turn out onto a plate with lemons facing up.
Beat mascarpone in a bowl to soften.
Add cream, vodka, icing sugar, and lemon juice.
Whisk mixture until soft peaks form.
Serve cake with cream, mint, and lemon zest.