Making a Fluffy Japanese Cake Roll involves several steps, but following them will lead you to success. Here’s how to do it:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a 10×15-inch baking pan with parchment paper.
2. Separate Eggs: In a mixing bowl, separate the egg whites from the yolks. Place the egg whites in a large bowl and the yolks in another.
3. Mix Egg Yolks: Add granulated sugar and vanilla extract to the egg yolks. Whisk until the mixture becomes creamy and pale.
4. Combine Dry Ingredients: Sift in the cake flour and mix until just combined. Add the milk and vegetable oil, stirring gently to incorporate.
5. Beat Egg Whites: In another bowl, whip the egg whites with a pinch of salt until soft peaks form. Gradually add the remaining sugar and continue whipping until stiff peaks form.
6. Fold Mixtures: Gently fold the whipped egg whites into the yolk mixture in three parts. Be careful not to deflate the batter.
7. Bake: Pour the batter into the prepared baking pan and spread evenly. Bake for 15-20 minutes or until the top is lightly golden and springs back when touched.
8. Cool: Once baked, remove from the oven and let it cool in the pan for 10 minutes. Then, invert onto a clean kitchen towel dusted with powdered sugar. Carefully peel off the parchment paper.
9. Prepare Filling: While the cake cools, whip the heavy cream with powdered sugar until soft peaks form.
10. Assemble the Roll: Spread the whipped cream over the cooled cake. Add any additional fillings, such as fresh fruit or chocolate. Starting from one end, carefully roll the cake using the towel to guide it.
11. Chill: Wrap the rolled cake in plastic wrap and refrigerate for at least 30 minutes to set.
12. Slice and Serve: Once chilled, slice the cake roll and serve it on a platter for everyone to enjoy.

Each of these steps is crucial for achieving the perfect Fluffy Japanese Cake Roll. The care taken in folding the mixtures and rolling the cake will ensure a beautiful final product.