In a medium saucepan, combine 1 cup of frozen blueberries, 1/2 cup of granulated sugar, and 1/4 cup of water. Cook over medium heat for about 10-15 minutes, stirring occasionally, until the mixture thickens and is bubbly. Once thickened, remove from heat and let it cool completely.

While the blueberry compote is cooling, preheat your oven to 350°F (175°C). Prepare three 6-inch round cake pans by lining the bottoms with parchment paper and lightly greasing the sides.

Separate 5 large eggs, placing whites in a large mixing bowl and yolks in a separate bowl. Beat the egg whites with 1/4 teaspoon of cream of tartar until stiff peaks form, about 4-5 minutes. Mix the egg yolks with 1/4 cup of milk, 1/4 cup of light oil, and 1 teaspoon of vanilla extract. Sift together 1 cup of cake flour and 1 teaspoon of baking powder, then whisk into the yolk mixture until smooth.

Gently fold the beaten egg whites into the yolk batter in three parts, being careful not to deflate the mixture.

Evenly divide the batter among the prepared cake pans. Place them in the preheated oven and bake for 25-27 minutes, or until the tops are lightly golden and a toothpick inserted in the center comes out clean.

In a chilled mixing bowl, combine 1 cup of heavy cream and 1/4 cup of powdered sugar. Whip the mixture until stiff peaks form, about 3-5 minutes. Gently fold in 1/4 cup of the cooled blueberry compote into the whipped cream.

Once the cake layers are completely cool, place one layer on a serving plate. Spread a generous layer of the blueberry whipped cream and add another layer on top. Repeat the process until all layers are stacked.

After chilling, use any remaining blueberry whipped cream to frost the top and sides of your Blueberry Chiffon Cake. Decorate with fresh or thawed blueberries and optional sprigs of thyme.