Level cake layers with a long serrated knife; place bottom layer on a 9-inch cake board or plate.
Spread 3/4 cup frosting over bottom layer; stack second layer and crumb-coat with 1/2 cup frosting. Chill 10 minutes.
Tint remaining frosting light yellow if desired; finish crumb coat and smooth with an offset spatula.
Press cookie halves upright around the cake edge, flat cream side out, spacing evenly.
Arrange emoji cookies on top in a circle or random pattern.
Use black icing to draw faces on any plain cookies and add sprinkles as needed.