Makes 30 medium-sized shells
Place butter and water in a saucepan and bring to a boil. Add the flour and the salt. Lower the heat and beat the mixture until it forms a ball and slides away from the sides of the pan. Remove from heat.
Add the eggs one at a time, beating hard after each addition until the dough is very smooth. Drop from a spoon on a greased baking sheet about 2 inches apart.
Bake 20 mintues in a preheated 400° oven. Then lower heat to 350° and bake 25 minutes more.
When puffs have cooled, cut off the tops and fill as follows:
Combine milk and cream in top of a double boiler and warm over low heat.
Sift the dry ingredients together. Add the milk and cream to them slowly, stirring constantly. Return this mixture to top of double boiler and boil until thick, stirring to keep smooth and to prevent scorching.
Beat the eggs until frothy. Add the cooked mixture to them. Return again to the top of the double boiler and cook a few minutes longer, stirring continually.
Let cool. Whip the heavy cream and fold into the mixture. Add vanilla. Fill the puffs, cover with their tops and serve.