Cream Corn Custard Cake

I wanted a thin layer of custard filling so I only use 1/2 portion for the custard filling and I added in extra cream corn. The surface is not smooth, why? Blamed it on my itchy hand lah. I tried to smooth the surface while it already half set. I shouldn't have do that in the first place as due to the extra cream corn which I added, the surface will appeared uneven. :(

Recipe

Ingredients
Base sponge:
240g optima flour
4 egg
60g water
60g corn oil

Cream Corn Custard:
450ml coconut milk
200g cream corn
350ml fresh milk
130g sugar
50g hoon kueh flour (green bean flour)
50g custard powder
2tsp instant jelly powder

Steps:
Base sponge:
1. Pour all the ingredients except oil into a cake mixer.
2. Whisk until thick and fluffy.
3. Add in the oil and whisk until well combined.
4. Pour batter into a lined 8" square tin.
5. Bake in a preheated oven 180C for 25-30mins.
6. Remove cake from pan and set aside to cool.
7. Peel off the top crust and slice sponge into two pieces.

Cream Corn Custard:
1. Mix all the ingredients except cream corn into a pot until well combined.
2. Cook over low heat until custard thicken, must stir at all the time.
3. Lastly, stir in cream corn and mix well.

Assemble cake:
1. Place a sponge cake at the bottom of a 8" square tin.
2. Pour half of the custard over the sponge.
3. Place another sponge over the custard and pour in the rest of the custard.
4. Smooth the surface and chill until set.