Preheat oven to 180°C (350°F). Brush a 24cm pie plate or quiche dish with melted butter.
In a saucepan, melt butter on medium-low heat. Continue to cook for about 5 minutes until butter starts to brown. Add the vanilla extract and salt. Mix. Remove from heat and cool completely.
Place almond meal in a large bowl. Add flour and icing sugar. Add the lemon zest and stir to combine.
In a separate clean dry bowl whisk together the egg whites until frothy. Add the egg whites to the flour mixture. Add the butter mixture and mix well with a wooden or silicone spoon.
Spoon the batter in the prepared baking plate. Sprinkle with nutmeg. Bake for 25 minutes until golden and cooked through when tested with a skewer. Remove and cool completely before slicing and serving.