In a large bowl, mix together 1/2 cup of sugar, cream of tartar and egg whites until stiff.
Take another bowl and combine the baking powder, salt and flour.
Using a separate bowl, mix together the butter and the remaining sugar. Add the lemon zest, lemon juice, vanilla extract and soured cream while mixing.
Now add the flour mixture, almonds and the rest of the egg whites while stirring.
Then add in the original egg mixture and stir well.
Pour into a large greased baking pan.
Place in an oven preheated to 350 F and bake for about 60 minutes or until brown.