Grease a slice tin (approx 28 x 18cm) and line with baking paper, leaving paper overhanging at sides to assist with removal of slice later.
Pre-heat oven to moderate (180 degrees celsius, fan-forced).
Beat the eggs on med-high for 5 minutes or until pale coloured and fluffy.
Add the sugar slowly while beating on low speed. Once added, beat on med-high speed again for one minute.
Mix in the dates and walnuts.
Sift the flour, baking powder and salt and fold into the mixture.
Add the butter and vanilla extract and stir to combine.
Pour mixture into slice tin and use a spatula to spread out evenly in tin.
Bake for 25-30 minutes or until a golden-brown colour and firm to touch.
Allow to cool to a warm temperature in the tin, then remove using the overhanging baking paper. Cut into squares and allow to cool completely on a cooling rack.