Grandma Eva's Sponge Cake

Recently received this email from my mom (I edited the title & text just slightly to eliminate ‘email-speak’ and protect identities) …

Suzie,
Was going through my recipe's looking for bar recipe's … and I found a recipe from Grandma for Sponge Cake with 12 egg yolks.  Don't know if you remember it - but I made it a few times - sponge cake is rich.  I like it plain, but I remember Dad liked it with a thin orange or lemon glaze.  So here it is:

Grandma Eva's Sponge Cake
3 cups Cake Flour
4 tsp. Baking Powder
1 tsp. Salt
12 Egg Yolks
2 Cups Sugar
1 Tbsp Grated Orange Rind
2 Tbsp. Lemon Juice
1 Cup Boiling water
Mix and sift flour, baking powder and salt - Beat egg yolks until thick and light colored.  Gradually add sugar, beating until very thick and light colored.  Beat in orange rind, lemon juice and boiling water.  Fold in flour and put in tube pan.  Bake 350 degrees for 50-60 minutes. Invert 1 hr.