Orange cake with passion fruit Swiss Meringue Buttercream

This recipe is from http://www.cakepaperparty.com/. I have used a number of the recipes and so far have loved them all. This one was a big hit with the family.

Orange Cake with Passion Fruit Buttercream
Ingredients

12 ounces (340 grams) unsalted butter, softened- 1 ½ cups/3 sticks
15 ounces (425 grams) granulated sugar- 2 cups
3 large eggs
2 tablespoons (30 milliliters) vanilla extract
1 ½ tablespoons (23 milliliters) finely grated orange zest lightly packed (I used tangerine)
1 tablespoon (15 milliliters) orange oil or orange extract
8 ounces (227 grams) cake flour*- 2 cups
4 ounces (113 grams) all-purpose/plain flour- scant 1 cup
½ teaspoon (5 milliliters) baking soda
1 ½ teaspoons (8 milliliters) baking powder
9 ounces (255 grams) plain low-fat yogurt- 1 cup
6 tablespoons (90 milliliters) orange juice
For the Passion Fruit Buttercream:
8 ounces (227 grams) egg whites separated from whole eggs or from a carton- 1 cup
16 ounces (454 grams) granulated sugar- 2 ¼ cups
½ ounce (14 grams) corn syrup- 1 tablespoon
16 ounces (454 grams) unsalted butter softened but not warm- 2 cups
1 tablespoons (15 milliliters) vanilla extract
2 teaspoons (10 milliliters) passion fruit paste ***see note
4 tablespoons (60 milliliters) orange juice
Instructions

Preheat oven to 350 F (177 C). Spray three 8-inch round cake pans with Baker’s Joy or grease and flour.
Beat butter and sugar for 2 minutes of mixer. Add orange zest, oil and vanilla and beat on medium-high speed for 30 seconds to infuse the butter with the flavors. Add eggs one at a time and beat until well combined.
Sprinkle in dry ingredients to distribute. Turn mixer on low and mix to moisten dry ingredients. Add half of yogurt and orange juice and beat on low until incorporated then and beat on medium-high for one minute until well combined and smooth. Add remaining yogurt and orange juice and beat on medium-high for about 30 seconds until smooth and well mixed.
Pour into prepared pans and bake for about 25-30 minutes until the cake is well done. Do not under bake or this rich cake will be over-moist and unstable. The cake should begin to settle back on itself on the edges (about 2-3 minutes beyond when a toothpick comes out clean). Cool 10 minutes in pan and then turn out to a cooling rack. Cool completely if using immediately, or wrap in two layers of plastic wrap if using later. This recipe makes three layers about 1 ¼ inches high each. Frost the cooled cake with Passion Fruit Buttercream or your buttercream of choice. Enjoy!
For the Passion Fruit Buttercream:
Whisk egg whites, sugar and corn syrup together in a microwave-safe bowl; make sure the mixture is well mixed so the sugar can protect the eggs from cooking. Heat the mixture in the microwave for 2-4 minutes on high in 30 second intervals whisking well after each 30 second heating. Heat until the sugar is dissolved and the mixture reaches 160ᵒ F/72ᵒ C. (Alternatively this step can be carried out in a double boiler over simmering water). Pour the syrup into a cake pan or shallow metal bowl and chill in the freezer for 20-30 minutes until it is quite cool (45-60ᵒ F).
Meanwhile, beat the butter in a mixer for 2 minutes on high until the butter is lighter in color and aerated. Add the cooled syrup in two additions to the butter beating 1 minute after each addition. Add the vanilla, passion fruit paste and orange juice and beat 30 seconds until smooth; can be used immediately.
You can store this buttercream at room temperature for 2 days, in the refrigerator tightly sealed for 2 weeks, or in the freezer for 2 months.
Passion fruit paste is very expensive. Since it is not something I will use often, I purchased (in the Spanish frozen food section) frozen passion fruit pulp and boiled it down to almost a paste consistency. Also did not use this buttercream recipe, I used one that uses less sugar and used the passion fruit to flavor it. This is the recipe I like to use: onehttps://fromscratchsf.wordpress.com/2011/03/08/tutorial-swiss-meringue-buttercream/