Line a 17X12" jelly/ sheet pan with parchment paper. Set aside.
In a mixing bowl add 2 eggs, 3 egg yolks and 1/2 cup sugar. With paddle attachment on, beat on medium to speed around 5 min until pale color and thickened. Add the vanilla extract and beat few more sec.
Stif flour and the cornstarch over egg yolks mixture and with a spatula gently fold it in.
Fold in the batter bits as well.
In separate grease free bowl, add 2 egg whites and 1tbsp of sugar. With a whisk, whip until firm peak form.
With spatula, fold the whipped egg whites into egg yolk mixture.
Pour cake batter into the prepare pan, spread it evenly and bake for 6-7 min until golden brown and, when touch it should spring back.
As soon as you remove cake from oven sprinkle with powder sugar and then invert the cake onto a clean dish towel. Remove parchment paper, sprinkle with more powder sugar, and roll up the cake with the towel. Place on wire rack to cool.
🔳Vanilla Buttercream
In clean bowl add the butter. With the whisk attached on to the mixer whip the butter for 2-3 min on medium to high speed.
Lower the speed and slowly add the sugar, 1/2 cup at a time.
When all the sugar is incorporated increase speed and whip for 2 more mins.
Add few drops of heavy cream until it reaches the consistency you desire.
Fold in sprinkles with spatula.
Gently unroll the cake and spread the buttercream evenly all over it.
Roll it again and place in the fridge for a couple of hours.
⬛️Decoration
Melt white chocolate in double boiler or microwave and pour it over the cake. Add more sprinkle like desire.
Let chocolate settle for a few mins and slice the cake.