Make the custard. Mix together the flour, cornstarch, and sugar with a whisk. Mix 25 g of milk, egg yolk, and then the remaining 75 g of milk.
Microwave at 600W for 1 minute, stir, then microwave for another 50~60 seconds. Stir, mix in the vanilla extract, tightly wrap with cling wrap, and let cool.
Make the cookie dough: Mix sugar into the butter. Add 1 whole egg and mix together. Mix in the almond powder. Add the flour in 3 batches and mix together each time.
Make the puff pastry: Sift the flour. Beat the egg.
Add butter and water to a pot on low heat and melt the butter. When the liquid begins to slightly bubble, add the flour, turn off the heat, and stir for 1 minute.
Turn the heat to low and knead it together for about 1.5 minutes with a large spoon, then turn off the heat. Preheat the oven to 200ºC.
Add the egg a little bit at a time and mix with each addition. Add the egg until the batter becomes thick and stays on the spoon for an instant before slo~wly falling off.
Spoon the batter onto the baking sheet and thinly layer the cookie dough batter on top of 3 of the batter for the normal puffs. (In the picture, the cookie ones are the 2 in the front and 1 in the back center)
Spray lightly with water, and bake for 17 minutes at 200ºC and then 10 minutes at 180ºC.
Whip sugar and heavy cream together. Cut the strawberries in half. Slice the banana and sprinkle lemon juice.
When the puff pastries have cooled, cut off the tops and place the custard, bananas, and strawberries on the bottom half. Spread the cream on the top half.
Push the top and bottom halves back together and if you want, dust with powdered sugar.