Preheat the oven to 350°F. Line a 10 by 15 inch jelly roll pan with parchment paper and lightly grease the parchment.
Place the egg yolks and 35 g of the granulated sugar in a bowl. Whisk until the mixture is pale, thick, and ribbons off the whisk, about 2 to 3 minutes.
Whisk the milk, vegetable oil, and vanilla bean paste into the yolk mixture until smooth and fully combined.
Sift the cake flour over the yolk mixture and gently fold with a spatula just until no dry streaks remain, then set the bowl aside.
In a clean bowl, add the egg whites and beat with a mixer on medium speed until foamy. Gradually add the remaining 35 g granulated sugar and continue beating until medium stiff peaks form.
Fold one third of the whipped egg whites into the yolk batter to lighten it, then gently fold in the remaining egg whites in two additions, keeping as much air in the batter as possible.
If using colored designs, tint a small portion of the batter with gel food coloring, pipe or spoon simple shapes on the prepared parchment, and freeze for 5 to 10 minutes before adding the remaining batter.
Pour the plain batter into the prepared pan, spreading it into an even layer that reaches all corners. Tap the pan firmly on the counter 1 or 2 times to release large air bubbles.
Bake for 10 to 12 minutes until the top is lightly golden and springs back when gently pressed in the center.
While the cake bakes, lay a clean kitchen towel on the counter and dust it evenly with powdered sugar.
As soon as the cake is done, run a knife around the edges, then invert the cake onto the prepared towel. Carefully peel off the parchment paper.
Trim a thin edge from all sides if they feel crisp, then starting from a short side, roll the warm cake and towel together into a tight spiral. Place it seam side down on a rack and let it cool completely.
Once cool, gently unroll the cake. Spread an even layer of whipped cream or buttercream over the surface, leaving a 1/2 inch border on the far short edge.
Scatter sliced fruit and sprinkles lightly over the filling, keeping the layer thin so the roll keeps its shape.
Reroll the cake without the towel, starting from the same short side, using gentle but firm pressure to keep the spiral tight. Place seam side down on a serving platter.
Chill the filled cake roll for at least 2 hours to set the shape, then, if desired, frost the outside with a thin layer of whipped cream or buttercream and decorate with more fruit, sprinkles, and colored details before slicing.