Preheat the oven to 400 degrees. Prepare a large baking sheet with parchment paper or line with a silicone baking mat.
In a small pot, bring the butter, milk, water, and salt just to a boil over medium-high heat. {Watch it carefully, dairy is notorious for bubbling over onto stoves!}
When it comes to a boil, remove from the burner and add in the flour. Stir, stir, stir with a wooden spoon until a thick paste forms. Return it to the burner and keep stirring until the paste pulls away from the sides of the pot and forms a dough. {This will only take a minute or two.}
Transfer the dough to a stand mixer fitted with a paddle attachment. Beat it for a minute or so just to cool it down, then add eggs one at a time, mixing until they are fully incorporated and you have a smooth dough.
Scrape the dough into a piping bag fitted with a round tip. {Or you can just use a zip top bag with the tip snipped.} Pipe about 1 ½ inch mounds of dough onto prepared baking sheet. Bake for 18-20 minutes until the mounds are puffed and golden brown. {You may want to tear one open to test and make sure that the middles are not too moist. If you under-bake them they will deflate a little.}
Remove the puffs from the baking sheet and cool on a wire rack.
Meanwhile, make the filling: Combine all ingredients in a medium bowl. Beat with a hand mixer until a whipped cream with soft peaks forms.