Preheat oven to 350 degrees. Butter a roll cake sheet pan and line with parchment paper. Whisk together yolks and 3 tablespoons sugar until the sugar is dissolved. Whisk in milk, vegetable oil and vanilla until smooth. Sift in flour and cornstarch and whisk until smooth.
In the bowl of a stand mixer, whip egg whites until frothy, then add cream of tartar. Whip at medium-low speed for 2 minutes, then gradually add remaining sugar. Whip on medium-high until stiff peaks form. Fold the egg white mixture into the egg yolk mixture.
Divide the batter and tint it as desired. Paint/pipe the batter into the pan. Tap the pan on the counter to avoid air bubbles. Bake for 20 to 25 minutes until fluffy. Cake will spring back when touched. Remove parchment paper, and cool cake on a drying rack covered with a towel.
Once the cake has cooled spread whipped topping onto 2/3rds of the cake surface and dot on the fruit!
Using the parchment paper to help roll the cake create a tight spiral and land the cake seam side down.
Tip #1: You can trace your design in pencil on the back of parchment paper if you want to create a precise design without the guesswork!
Tip #2: Hit your tray on the countertop a few times to make sure that all of the air bubbles in your cake come to the surface.
Tip #3: Remove the parchment paper from your cake as soon as it cools, about 5 minutes after it comes out of the oven and place it on a new piece of parchment. This will help you roll the cake without the parchment steaming the surface of the cake and causing soggy texture.