Preparing the Sponge Cake:

1. Preheat the Oven: Set your oven to 375°F (190°C) and line a 10×15-inch jelly roll pan with parchment paper.
2. Mix Dry Ingredients: In a bowl, whisk together flour, baking powder, and salt.
3. Beat the Eggs: In a separate bowl, beat the eggs with sugar until pale and fluffy. Add vanilla extract and mix well.
4. Combine and Fold: Gradually fold the dry ingredients into the wet mixture, being careful not to deflate the batter.
5. Bake: Spread the batter evenly in the prepared pan and bake for 10-12 minutes, or until the cake springs back when touched.

Rolling the Cake:

1. Dust with Sugar: Sprinkle powdered sugar on a clean kitchen towel.
2. Transfer and Roll: Turn the warm cake onto the towel, peel off the parchment paper, and roll it up gently with the towel. Let it cool completely.

Making the Raspberry Filling:

1. Cook the Filling: In a saucepan, combine raspberries, sugar, cornstarch, and water. Cook over medium heat until thickened.
2. Strain for Smoothness: Optional—strain the mixture to remove seeds. Let the filling cool.

Assembling the Cake Roll:

1. Unroll and Spread: Gently unroll the cake and spread the raspberry filling evenly.
2. Re-roll the Cake: Roll it back up without the towel, taking care to keep the filling inside.
3. Chill: Wrap the roll in plastic wrap and refrigerate for at least 1 hour.

Finishing Touches:

1. Whip the Cream: Beat heavy cream with powdered sugar and vanilla until stiff peaks form.
2. Decorate: Spread whipped cream over the roll, dust with powdered sugar, and add your chosen decorations.