Combine butter, milk, water, salt, and sugar in a small pan and heat until just before boiling.
Add cake flour and use a wooden spatula to knead very well.
As it starts to take shape, continue to knead into a round clump for about a minute. The dough shouldn't stick to the bottom of the pan, and you'll see a white film at the bottom.
Remove from heat and slowly add beaten eggs. Knead very well. It'll get pretty heavy, so hang in there!
As shown in the picture, if you scoop with the spatula and the dough drips down in a triangle shape, this is the best! *If the dough is too soft or too hard, it won't expand!
Put the dough in an icing bag and use it to create 4 cm round drops on a baking pan with a cooking sheet spread across. You can also use a spoon to create the rounded shapes.
If you've squeezed the dough with an icing bag, there may be tips on the squeezed dough. Wet your fingers and flatten the peaks.
Use a spray bottle filled with water to moisten. Moistening adjusts how they expand.
Bake in a preheated over at 220℃ for 10 minutes, then drop the heat to 170℃ and bake for 15 minutes. Then leave for 5 minutes, take out of the oven, and cool in a rack, etc. Do not open the oven while baking!! They'll deflate in an instant!!
Then slice the top and fill with custard cream (Recipe ID: 438020) and whipped cream, and they're finished.
If you squeeze out the dough in a line, you could make eclairs.
Story Behind this Recipe
This is a recipe I finally came up with after many repeated failures.
In step 3 if you don't properly heat the flour it won't expand later! Adding milk gives the dough it's well-defined feel. If you don't put in the cream right before eating, then it'll become soft! When making these as a present, prepare the cream and the dough separately, and put the cream in right before eating. That's best!