Lemon cake with watermelon

Crush the biscuit and knead it with the butter, put it in the bottom of an individual mould (ring) with a thickness of 2-3 mm. Leave to cool in the fridge and in the meantime mix the lemon, condensed milk and 2 sheets of gelatine. Cover the mould minus 5 mm, which we will cover in turn with the watermelon jelly that we will have made with the juice and the remaining 2 sheets.