We'd eaten this recipe for 40 years at my folks' before we discovered the "proper" name for them is "Pommes Dauphine", and they were quite popular in Eastern Europe too.
Step 1: First collect the ingredients
1/4 pint 145mL of water
3 eggs (1 yolk and 2 whole eggs)
2.5 oz (71g) of plain "all purpose" flour.
3 oz (85g) of butter (1 oz and 2oz)
Step 2: Make mashed potato
Step 3: Make choux pastry
Bring 1/4 pint of water gently to the boil, melting 2oz of the butter into the warming water.
Step 4: Choux 2
Step 5: Choux 3
CHILL the paste (this is important)
Step 6: Back to the mash
Season with salt and fresh ground black pepper, to taste.
Once mixed, fold in the choux mixture.