1. Preheat oven to 170°C conventional (150°C fan forced). Grease and line base of a 28x18cm slice pan.
2. For base: Combine all ingredients in food processor and blend until mixture just comes together. Press into pan, bake for 12–15 minutes or until golden brown.
3. For the filling: In a clean food processor bowl, blend the cream cheese and ricotta until smooth. Add remaining ingredients and blend until very smooth. Pour over the base and bake for 30-35 minutes (170°C conventional or 150°C fan forced), or until the filling is just firm. Turn off the oven, leave door ajar for 10 minutes then remove slice from oven.
4. For the topping: While the filling is baking, combine the Chelsea Icing Sugar, lemon juice and eggs in a large bowl placed over a smaller saucepan of barely simmering water. Whisk for about 4-5 minutes until mixture thickens then remove from the heat and whisk in the butter a little at a time until smooth. Allow to cool. Gently spread over cheesecake filling. Refrigerate for 1-2 hour, or until cheesecake is firm to cut.