In a large mixing bowl, combine the yellow cake mix, pure almond extract, vegetable oil, and egg whites. Beat on medium speed for about 2 minutes until smooth.

Preheat your oven to 350°F (175°C) and grease a cake pan. Pour the batter into the prepared pan, smoothing the top. Bake for approximately 35 minutes.

Remove the cake from the oven and cool in the pan for about 10 minutes. Flip onto a wire rack to cool completely.

In a saucepan over medium heat, whisk together all-purpose flour and milk until thickened. Stir continuously for 5-7 minutes to avoid lumps.

In a mixing bowl, beat the softened unsalted butter until fluffy. Gradually add the cooled flour mixture while continuing to beat until light and airy.

Once the cake is cooled, apply a generous layer of buttercream frosting on top and decorate as desired.