Flourless Lemon Polenta Cake with Limoncello Syrup

Name: Flourless Lemon Polenta Cake with Limoncello Syrup
Yield: Serves 10
Cuisine: Italian
Ingredients: 1 tsp baking powder; 200 g ground almonds; 100 g instant polenta; 275 g unsalted butter, softened, plus more for the tin; 2 unwaxed lemons, very thinly sliced; 2 tbsp limoncello; 100 g caster sugar; 5 eggs, lightly beaten; finely grated zest of 2 large unwaxed lemons and juice of 1; 250 g golden caster sugar; ½ tsp salt