Preheat oven to 180 degree C. Grease two 9 inch round pan with oil and dust it with flour. Coat on all sides and set aside.
Now take flour, baking powder, salt in a bowl and mix well. set aside.
Now take egg white in a bowl and use a electric beater and whip till peaks form.
Take butter, sugar and vanilla in a bowl and use a beater to whip it till creamy.
Now add in sourcream and whip till creamy. Now add in half of the flour mix and half of the milk and fold gently. Now add the remaining flour and milk and fold gently.
Add in sprinkles and mix gently.
Finally fold in egg whites in portions and gently mix well.
Spoon this into two pans and bake for 30 to 35 mins. Insert a toothpick to check whether it is coming out clean or not. If it comes clean then it is cooked.
Now remove the cake from oven and cool completely.
Prepare a batch of vanilla buttercream.
Place a cake on the cake stand, Now take some of the buttercream and spread evenly. now place another cake on top and top with some buttercream. Now spread frosting all over the cake and spread evenly.