Preheat oven to 375 degrees. Bring butter, sugar, salt, and 1 cup water to a boil in a saucepan over medium-high heat, stirring occasionally. Remove from heat. Stir in flour. Return to medium-high heat; cook, stirring constantly, until mixture pulls away from sides, about 3 minutes.
Transfer to the bowl of an electric mixer fitted with the paddle attachment; mix on low speed until slightly cooled, about 1 minute. Raise speed to medium. Add whole eggs, 1 at a time, mixing well after each addition. Test batter by touching it with your finger and lifting to form a soft peak. If a soft peak does not form, mix in egg white a little at a time until it does.
Transfer to a pastry bag fitted with a 9/16-inch plain round tip (such as Ateco No. 807); set aside. Dip a 1-inch round cookie cutter in flour; mark circles 1 inch apart on baking sheets lined with nonstick baking mats or parchment paper. Pipe batter into circles to fill. Gently smooth and round tops with a moistened fingertip.
Bake until golden brown, about 20 minutes. Transfer sheets to wire racks to cool.
Poke a small hole in bottom of each choux with a 5/16-inch French tip (such as Ateco No. 863). Transfer 1 cup pastry cream to a pastry bag fitted with a 5/16-inch plain round tip (such as Ateco No. 802). Fill each choux with pastry cream.
Fold remaining 3/4 cup pastry cream into whipped cream until nearly incorporated but streaks are still visible. Put 6 filled choux into each serving dish; top with whipped cream, dividing evenly. Garnish with rose petals if desired.