Preheat oven to 325 degrees. Grease and flour tube pan or 10 or 12 cup bundt pan.
In a microwave safe bowl, pour heavy cream over 5 oz. white chocolate and microwave for 30 seconds. Stir, then continue in smaller increments until the chocolate is almost melted. Stir until smooth and completely melted and well combined.
In a separate bowl whisk the cake flour, salt, and baking powder for 30 seconds to combine, set aside for later.
Cream the butter on medium speed with an electric mixer (use a paddle attachment if using a stand mixer). Add the vanilla extract. Gradually add the sugar and beat until lightened in color and fluffy 3 to 5 minutes.
Add the room temperature eggs one at a time, waiting a few seconds after each addition until yolk has blended.
With the mixer on low speed, add the flour mixture alternately with the white chocolate/cream mixture to the butter, sugar, egg mixture. Begin and end with the dry ingredients. I add the dry ingredients 3 times and wet ingredients twice. Mix just until blended.