Add butter, milk, water, sugar, and salt into a medium sauce pan. Cook over medium heat until it just starts to boil.
Remove from heat, add in all the flour and mix together.
Place back onto the heat and cook for another 1-2 minutes until the dough comes together like a ball.
Move the dough to a large mixing bowl and mix to cool down.
Add in each of the 4 eggs, one at a time. Mix in between each egg addition until combined.
Pipe the dough into small (1 1/2") mounds using a gallon ziplock or piping bag. Place at least 1" apart.
Bake at 425ºF for 10 minutes. Decrease bake temp to 325ºF and bake for another 20-25 minutes until everything is golden brown.
Allow puffs to completely cool on a wire rack.
Once cooled, cut 1/3 of the way up from the bottom, add whipped cream filling, and top with powdered sugar.