Preheat the oven to 180 °C convection oven.
Separate the eggs and beat the whites with the lemon juice until stiff. Add the sugar and beat again until stiff.
Whisk the egg yolks. Sift the flour with the cornstarch and fold into the beaten egg whites alternately with the egg yolks.
Put 1/5 of each mixture in a small bowl and color them all (light green, dark green, red, light red, orange).
Pour each batter in layers into the jars (3/4 of the way up) and bake in the oven for about 25 minutes.
Take out and let cool.
Serve the Rainbow cakes in the glass garnished with whipped cream and almonds as desired.