Lemon Cream Cheese Roll Cake (檸檬忌廉芝士卷蛋)

Ingredients
Sponge Cake
4 Egg whites
40g of Caster sugar
4 Egg yolks
40g of Caster sugar
1 - 2 drops of Vanilla essence
2 tsp of Lemon juice
45g of Cake flour
2 tbsp of Hot water
1 tbsp of Caster sugar

Cream Cheese Filling
1 (8-ounce) package cream cheese, softened
1/2 cup sugar
1 tsp of Vanilla essence
3 tbsp of Lemon juice

Steps
Cream Cheese Filling
1. Beat cream cheese at medium speed with an electric mixer until creamy; gradually add sugar, lemon juice and vanilla, beating well.

Sponge Cake
1. To make the meringue, beat egg whites and sugar in a mixer on low speed. When it starts to get frothy, increase to medium. Beat till stiff peaks form. 
2. In a separate bowl, beat the egg yolks, caster sugar, lemon juice and vanilla essence until mixture becomes creamy. 
3. Sift in the cake flour and mix till combined. 
4. Add 1/3 of the meringue in Step 1 to the batter in Step 3. Use a balloon whisk to mix, and knock against the side of the bowl to let the mixture fall. Repeat till combined, all the while being careful not to break the air in the meringue. 
5. Add another 1/3 of the meringue and fold in with a spatula. Use the same fold-and-knock motion. When combined, add the final 1/3 of meringue and fold-and-knock till combined. The batter should be smooth and shiny. 
6. Transfer the batter to a baking sheet lined with parchment paper. Gently spread the batter evenly with a spatula. Be careful not to break the air when spreading!
7. Bake in a preheated oven at 170°C for 25 minutes. Let it cool before removing from the parchment paper. Trim off the sides (don't throw them away!)
8. Mix hot water with sugar to make the sugar syrup. Spread the sugar syrup on the cake to keep it moist.
9. Spread a layer of cream cheese filling on the sponge cake. 
10. Make 3 small incisions on each side of the sponge cake and roll gently. Wrap the cake in parchment paper and chill it in the fridge for 1 - 2 hours. 

Reference
1. http://www.myrecipes.com/recipe/cream-cheese-filling-3