Citrus Ricotta Slice

200g packet low fat butternut cookies, crushed
2 T butter, melted
250g low-fat ricotta cheese
250g low-fat cream cheese
½ C caster sugar
1/3 C lemon juice
grated rind of 1 lemon
½ t vanilla essence
1 egg
1 egg white

Combine biscuits and butter. Line 18x28cm slab tin with baking paper. Firmly press mixture into base. Refrigerate 30 mins or until firm. Heat oven 180°. Beat remaining ingredients, except egg, with electric beater until smooth. Add egg and mix well. Pour over base. Bake 30-35 mins or until set. Allow to cool in tin before slicing.