Preheat oven to 180C (350F) and grease and line a 24cm spring form pan.
Using a stand mixer, beat egg whites with salt until firm peaks form. Gradually rain in the brown sugar and add the vanilla (if using). Beat until the mixture is glossy.
Gently fold nuts through the meringue mixture and spoon into prepared tin, smoothing the top.
Bake for 50 – 60 minutes or until top is golden brown and the pav has started to shrink away from the sides of the tin. It will still feel soft but will harden a little as it cools. Cool in tin.
Stir yoghurt and sour cream until just mixed. Serve slices of pav with cream mixture passed separately.