Preparing the custard (can be prepared one day ahead):
Beat the egg yolks with a fork. Add flour and add in 1/2 of the whole milk and continue to whisk until smooth
In a medium-size saucepan, add sugar, vanilla extract and the rest of the milk and heavy cream. Cook on medium to low heat until the sugar started to melt. Slowly add in the egg mixture while the other hand continue to stir. You will know when the mixture started to thicken, it will get heavy and smooth. Continue to stir until the custard is thickened. It took me about 15 minutes to get to the custard consistency. Remove from the heat and let the custard cool down completely. Cover with a plastic wrap touching the custard (to prevent skin from forming) and keep in refrigerator until ready to use
Making choux pastry:
Preheat oven to 375 F. I have a conventional bottom heat oven no fan. If yours are convection , you may want to lower the temperature by about 15-20 degrees.
Beat the eggs in a bowl with a whisk. It is very important that the eggs are not cold from the fridge. They need to be at room temperature
In a medium saucepan, add water and butter. Bring to a boil to melt the butter and then lower the heat to the lowest and add flour and salt all at once and continue to stir vigorously until the mixture is well blended. Keep stirring for another minute or two to dry the dough. The dough should be smooth and shiny and you can see a layer that coat the bottom of the pan. Remove from the heat and let it cool down for about 3 minutes
Add 1/4 of the egg and keep whisking. They will appear separate and look like big blob of mess. Just keep stirring and add another 1/4 and continue to gradually add as you stir until you get a paste consistency. You may not need all of the eggs or you may
The dough consistency you are looking for:
You can use your index finger to draw a line on the dough paste. The side of the line should maintain its shape. If it fall down, your dough is too runny already. You can also do a "V" tests. When you pull the dough up, it should drop down forming a "V" shape trail hanging down from your spatula. If it is, the dough is on the right consistency and you can stop adding egg. If it doesn't drop down at all, it's too thick. Beat another egg and try add half of the beaten egg and mix again and do the same "V" test until you reach that consistency I describe or the finger test
At this point, you can choose to use a large tipped nozzle with a piping bag or use two spoons to drop the dough on baking sheet lined with parchment paper. I recommend using a piping bag for better shape.
Transfer the dough to the bag and pipe about 2-inch in size. Hold the bag straight and pipe upward. The tip should stay in touch with the dough paste. Make sure you pipe it "tall", not wide to the side. Make sure you have about 1-inch gap in between as the dough will expand a bit as it bakes. If you use spoons, just gently drop the dough on baking sheet lined with parchment paper. Drop them "tall". Dip your finger in water and smooth out the top of the dough so the top won't burn during baking
Mist the tray with some water or drop some water droplets on the pan. This will turn into steams and help the choux to expand while baking
Pop this inside the oven (middle rack) and bake for the next 25-30 minutes (the time is just a reference, you may need longer if your choux are bigger). DO NOT open the oven door during this baking time. DO NOT open the oven door for the first 25 minutes. Once they are done, I turn off the oven and let them sit in there for about 10 minutes to let the choux dry up. Then remove from the oven, use a sharp paring knife to poke small holes on bottom to allow the steam to escape and cool on a wire rack completely
Slice the choux pastry in half horizontally and top with 1-2 Tbsp of custard cream and then top with the other half. You can also pipe the filling for some aesthetic if you choose to by poking the bottom with the piping tip and squeeze the filling in there. Sprinkle with some confectioners sugar if you going to serve it immediately. I recommend not to sprinkle with the sugar and keep them in the refrigerator as they will become "wet". You can drizzle or dip the choux pastry with melted chocolate if you choose to
I only assemble as many as we want to eat and refrigerate the choux pastry and filling separately. Read the "frequently asked questions" in this post up there for more detail