Preheat oven to 400 degrees. Line two baking sheets with parchment paper or baking mats. Set aside.
In a medium saucepan, heat butter, sugar, salt, and water together over medium-high heat until it boils. Immediately add all of the flour and stir with a wooden spoon. Continue to stir over heat until a firm forms on the bottom of the pan. Remove from heat and transfer dough to a medium bowl to cool down for 3 minutes.
Once slightly cooled, add 1 egg to dough and stir vigorously until combined into dough. Repeat with rest of eggs, one at a time.
Transfer mixture to a large pastry bag fitted with a large piping tip. Pipe 1 1/2 inch rounds onto prepared baking sheets (about the size of a macaron). Make sure to space out about 2 inches apart.
Bake in preheated oven for 15 minutes and then rotate to bake for another 15 minutes. The dough should be puffed and browned on top. Remove from oven. Using a sharp knife cut a small slit in the top or sides of the puff to allow the steam to escape. Let them cool completely.
Cut each puff in half. Dip the top of the top half into the cooled caramel sauce. Spoon the whipped cream (recipe below) onto the inside of the bottom half of the cut puff. Slice the bananas into 1/2-inc slices. Place one slice on the whipped cream. Top with the top half of the puff. Repeat with the rest of the puffs, salted caramel, banana slices, and whipped cream. Serve immediately or within 12 hours.