Blend the butter and sugar till it forms a creamy texture. Add the egg whites and flour slowly and mix well to make the batter. Now divide the batter into two bowls. Add red and pink color in each bowl. Pour them in two separate piping bags.
Now take a baking tray and lay a parchment paper. Make the designs of the red hearts and pink dots using the decoration batter. Keep this tray in the freezer for 10 minutes.
To make the chocolate cake sheet, take two bowls. Break in the eggs with the egg whites in one bowl and the yolks in the other. Add 1/4th cup of sugar and cream of tartar to the egg whites and blend till its fluffy.
Add the remaining 1/4th cup of sugar to the egg yolks and blend until creamy. In this add the butter and the cocoa powder. Mix well with a spatula. Gently fold 1/2 cup of flour till everything is well combined. The roll cake batter is now ready.
To assemble, take out the tray from freezer and pour this roll cake batter over the prepared hearts and dots and spread evenly. Meanwhile preheat the oven to 180 degrees Celsius. Bake this for 7 minutes, since it's a cake sheet it will bake fast.
Take the tray out and put a parchment paper over the prepared cake sheet and another tray over and flip it. Peel off the parchment paper over the top and again flip it over to a towel or parchment paper and roll it carefully when its warm. Roll from the side of the cake where there is no design.
After sometime open the roll cake and add some whipping cream or white frosting inside and spread evenly and add some strawberries and roll back again.