Butterscotch Chiffon Cake with Penuche Frosting

I ran across this recipe in our monthly food magazine "Relish."  A chiffon cake is a cross between a traditional layer cake and an angel food cake.  It's super light but not as airy as an angel foodcake.  The rich penuche frosting complements the light cake.

BUTTERSCOTCH CHIFFON CAKE with PENUCHE FROSTING

Cake:
2 1/4 cups cake flour
3 tsp baking powder
1 tsp salt
2 cups brown sugar, lightly packed
1/2 cup vegetable oil
5 egg yolks
3/4 cup cold water
2 tsp vanilla extract
6 egg whites
1/2 tsp cream of tartar

Penuche Frosting:
2 2/3 cups brown sugar, lightly packed
2/3 cup milk
2/3 cup butter (10 2/3 to 11 Tbsp)
1/4 tsp salt

To make the penuche frosting, combine all ingredients in a saucepan; cook, stirring constantly, over low heat until combined, then bring to a full boil. Boil 7 minutes; remove from heat. Let cool completely. Chill 2 hours. Beat until thick and creamy. Spread over sides and top of cooled cake.
 Preheat oven to 325F.

Whisk together the flour, baking powder, and salt.  Add brown sugar and mix well.  Add oil, egg yolks, cold water, and vanilla; beat until smooth

Beat egg whites with cream of tartar until stiff peaks form.  Gently fold into batter.

Pour batter into ungreased 10" tube pan; bake 55 minutes or until the top springs back when lightly touched.  Invert cake and let it hang upside down on a bottle (I used an empty wine bottle) until completely cooled.

Loosen sides with a knife or spatula, then turn pan over and knock pan to release cake.

Recipe Source: Relish Magazine, April 2014, p. 15