Preheat the oven to 400 degrees F. Line a large baking sheet with parchment paper or a silicone mat; set aside.
Using a large sauce pan, bring the water to a boil over high heat. Add the butter. Once the butter is melted, stir in the sugar and salt. Reduce the heat to medium and mix in all of the flour at once, stirring with a wooden spoon until the mixture forms a dough. Remove the pan from the heat and let sit for 2 minutes.
Beat in the eggs, one at a time, until each egg is fully incorporated and the dough is shiny and smooth. The dough will separate after each addition, but continue to beat until it comes back together. This will take some powerful elbow grease. Alternatively, use a food processor to mix the dough and all of the eggs at once, if desired. Either way, the dough should be shiny, smooth and thick when mixed well.
Spoon or pipe 8 to 9 mounds of the dough onto the prepared baking sheet, about 1 to 2 inches apart. Smooth the top of each mound with your finger. Bake in the preheated 400 degree oven for 15 minutes. Reduce the oven temperature to 350 and bake for another 30 minutes, or until the mounds are puffed and golden brown. Remove from the oven and allow to cool completely before filling.
To make the filling, whip together the mascarpone, heavy cream, sugar and vanilla until stiff peaks form.
To assemble, slice the puffs in half and spread filling on the top of the bottom half. Layer with a few sliced strawberries. Spread another layer of filling on the bottom of the top half, then place over top of the strawberries. Repeat with remaining puffs and cream. Dust the plated puffs with powdered sugar and chill in the fridge for at least 1 hour before serving.