Preheat the oven to 175 degrees Celsius.
Line or grease a loaf pan.
Separate the eggs into two separate bowls (making sure the bowl for the egg white is well cleaned).
Add sugar to the egg yolks and whisk until fluffy and turns pale. Take 3-4 minutes.
Add the ricotta, greek yogurt, apple sauce, lemon juice, stevia vanilla drops and pistachio butter. Whisk until incorporated and you have a smooth batter.
Combine oat flour, corn flour, baking powder and baking soda in a separate bowl. Add the dry ingredients little by little to the wet ingredients mixing gently inbetween.
Fold in chopped pistachio nuts.
Clean and dry your whisk well.
Add a pinch of to the egg whites and whisk the egg whites until white, fluffy, shiny and stiff peaks start to form.
Gently add 1/4 of the egg whites to the batter gently folding in. Then repeat with the remaining egg whites folding them in very gently just until combined.
Pour the batter to the prepared loaf pan, bake in the oven for 35-40 minutes, or until a toothpick comes out clean.
Remove from the oven, let it cool for 10-15 minutes. Then remove from the pan and let cool completely.
When the cake has cooled completely mix cream cheese, greek yogurt and powdered sugar until slightly fluffy and smooth. Spread over the cake and sprinkle with chopped pistachio nuts on top.