1. Place the butter, water and salt in a saucepan and bring to the boil. Stir the sugar into a bowl with flour.
2. When the water is boiling, pour the flour all at once into it, turn down the heat and stir energetically until the flour is absorbed and the dough forms a ball pulling away from the sides.
3. Take it off the heat and add the eggs, one by one, beating them in with a handheld mixer or simply a wooden spoon. The batter will end up smooth and glossy.
4. Transfer it into a piping bag, or just use two spoons to shape the pastries.
5. Preheat the oven to 200C/400F/gas 6. Grease a baking tray lightly with butter.
6. Pipe the buns onto the tray in blobs about 3-4cm (1 ½ in) or bigger if you prefer. Smooth them out with fingers dipped in water, if necessary.
7. Bake for 30-35 minutes until golden brown. Leave them in switched off oven for another 5 minutes, to ensure they dry well. Transfer them onto a wire rack and pierce a couple of holes in the bottom of each bun to let out the steam. They can be stored in an airtight box for a couple of days or frozen for longer. Crisp them up, or defrost, in a warm oven for a few minutes.
8. To make up the ice cream sandwiches, slice the choux buns in half horizontally, fill the bottoms with a scoop of ice cream each, decorate with sprinkles or drizzle with sauce and cover with the lids. Serve immediately.