Pour cake mix and ground almonds into a large bowl, add milk, oil and egg yolks. Beat on low speed until blended, then beat on medium speed for 2 minutes.
Divide batter between the three prepared pans. Set aside.
In a bowl, whisk egg whites until foamy, continue whisking gradually adding 1 cup of sugar until stiff peaks form.
Gently fold in sliced almonds.
Spread mixture evenly over the cake batter in pans.
Bake as directed on package, approximately 25 - 30 minutes or until toothpick inserted in centre comes out clean.
Cool 20 minutes, remove from pans.
Cool completely before you put the filling between the layers.
Filling and decoration:
Whip cream, sugar and vanilla until soft peaks form. Place one cake layer on serving plate; spread one half of the cream on cake layer. Put second layer on top, repeat the process and place third layer on top.