Preheat oven to 220°C and line a baking tray with baking paper.
Boil 125ml water, butter, and salt in a pan for 1 minute.
Remove from heat, add flour, and beat until the mixture is smooth and leaves the pan sides.
Cool dough for 3 minutes in a mixer then beat in eggs one at a time until glossy.
Pipe 1.5cm blobs onto the tray leaving 3cm gaps and smooth tops with a wet finger.
Bake for 12 to 15 minutes until golden-brown and then let cool.
Blend smoked salmon, cream cheese, and 150g crème fraîche with lemon juice and pepper until smooth.
Chill the salmon mixture in a piping bag until ready.
Whisk remaining crème fraîche with lemon juice and prep a bowl of chopped chives.
Stack watermelon and feta cubes garnished with basil and a drizzle of vinegar.
Pipe salmon filling into the bottom or top of each cooled choux bun.
Dip bun tops into seasoned crème fraîche then into chives and serve.