In a medium saucepan, combine frozen blueberries, granulated sugar, and water. Simmer over medium heat for about 10-15 minutes, stirring occasionally until the mixture thickens and coats the back of a spoon. Remove from heat and allow it to cool completely.

Preheat your oven to 350°F (175°C). Line three 6-inch round cake pans with parchment paper.

Carefully crack the large eggs, separating the yolks into one bowl and the whites into another.

Using a clean electric mixer, beat the egg whites on medium speed until frothy. Add cream of tartar, then continue whipping until soft peaks form.

In a large mixing bowl, whisk together the egg yolks, milk, oil, and vanilla extract until well combined. Sift in the cake flour and baking powder, mixing gently until the batter is smooth.

Gently fold one-third of the whipped egg whites into the yolk mixture to lighten it. Carefully fold in the remaining egg whites, mixing until just combined.

Divide the cake batter evenly among the prepared pans. Bake in the preheated oven for 25-27 minutes or until golden.

In a mixing bowl, combine heavy cream, powdered sugar, blueberry compote, and vanilla extract. Beat until stiff peaks form.

Once the cakes are completely cool, layer them on a serving platter, spreading blueberry whipped cream and drizzling with blueberry compote between layers.

Chill the assembled cake for about 30 minutes. Decorate with fresh or thawed blueberries and optional sprigs of thyme.