Cut a 9-inch circle from cardboard, and cover with foil.
Set the circle on a board near the stove.
Have the filled cream puffs close at hand.
Cook corn syrup in the top of a double boiler over high heat until candy thermometer reaches hard-ball stage (240°F), or until a small drop of the syrup forms a soft ball in cold water.
Set pan over boiling water.
To build the pyramid, lightly dip the bottom of a cream puff in syrup and set on the edge of the circle, syrup-side down.
Repeat with 9 more puffs, forming a ring.
For the second row, arrange a slightly smaller ring of puffs over the spaces between the puffs of the first row, inclining the second row slightly inward.
Fill in the center with more puffs, for support.
Continue building the pyramid in decreasing rings (see color illustration), filling in center for support as needed, until you have completed 8 rows.
Top with one puff.
Sprinkle the Croquembouche lightly with 1 /4 cup sifted icing sugar.
To serve, lift one or two puffs at a time off the pyramid, starting from the top.
Note: If syrup begins to thicken before pyramid is completed, add a teaspoon of water and stir over low heat.
Do not let syrup burn.