How to make chocolate chiffon cake

Ingredients

• 2/3 cups (160g) water, room temperature
• 6 tablespoons (74g) oil, flavorless such as canola or veg
• 4 large (80g) egg yolks
• 1 1/3 cups (160g) cake flour
• 1/2 cup (44g) cocoa powder, Dutch-processed*
• 2/3 cup (132g) white granulated sugar ( for flour )
• 1 1/2 teaspoon baking powder
• 1 teaspoon kosher salt (I use Diamond Crystal)
• 4 large (120g) egg whites
• 1/4 teaspoon cream of tartar
• 8 tablespoons (100g) white granulated sugar ( for meringue )