01 - Preheat the oven to 325°F. Grease a 2-quart baking dish with butter.
02 - Combine milk, cream, and butter in a medium saucepan over medium heat. Stir until butter melts and mixture is warm but not boiling. Remove from heat.
03 - Whisk egg yolks with 1/4 cup sugar, vanilla extract, cornstarch, and almond flour until smooth.
04 - Gradually whisk warm milk mixture into egg yolk mixture. Return to saucepan and cook over low heat, stirring constantly, until slightly thickened for 3-4 minutes. Remove from heat and cool for 5 minutes.
05 - Beat egg whites with cream of tartar and salt until soft peaks form. Gradually add remaining 1/4 cup sugar and beat until glossy stiff peaks form.
06 - Gently fold cooled custard into beaten egg whites in three additions, maintaining airy texture.
07 - Pour batter into prepared baking dish.
08 - Bake for 35-40 minutes until puffed, lightly golden, and just set in center.
09 - Remove from oven and cool for 10 minutes. Dust with powdered sugar and garnish with berries or mint if desired. Serve warm or at room temperature.