Preheat the oven to 180 °C (fan 160 °C). Grease and line a 23 cm springform tin with baking paper.
In a large bowl, use electric beaters to beat the ricotta and sugar until smooth and creamy.
Add the eggs and beat until mostly combined — the mixture may look a little curdled; that’s fine.
Mix in the melted butter, lemon zest, lemon juice, and vanilla extract.
Sift the flour, baking powder, and salt over the wet ingredients. Gently fold through by hand until just combined.
Pour into the prepared tin and smooth the top.
Bake for 45–50 minutes, or until golden and a skewer inserted in the centre comes out clean.
Allow to cool in the tin for 10 minutes, then transfer to a rack.
Once cool, dust with icing sugar before serving.