Step 1Position a rack in the upper third of the oven and heat the oven to 400 degrees. In a small saucepan, bring one-half cup water, butter, salt, sugar and white pepper to a boil, and simmer until the butter is completely melted and the mixture looks milky, about 2 to 3 minutes.
Step 2Remove the pan from the heat and all at once dump in the flour. Stir until a rather firm ball forms.
Step 3Dry the dough by returning the pan to medium-low heat and cook the dough, stirring constantly, flattening the ball to expose as much of the surface as possible to the heat. Cook until you see little bubbles of butter oozing from the paste and a sandy film of paste appears on the bottom of the pan, 5 or 6 minutes.
Step 4Remove from the heat and beat in the eggs, about a third at a time, stirring briskly to incorporate the egg into the dough as quickly and thoroughly as possible before adding another portion of egg. Stir vigorously. At first, the mixture will loosen and separate, but as you continue beating, it will come back together, thicken and become shiny and sticky.
Step 5Butter a cookie sheet generously and rinse it under cold water. (The water will evaporate while the puffs bake and prevent the bottoms from scorching.) Fit a plain nozzle into a pastry bag and fill the bag with the dough. Pipe balls about 1 inch in diameter onto the cookie sheet, leaving about 2 inches in between for expansion during cooking. You can also use two spoons to scoop out the dough and form it into balls.
Step 6Bake the puffs until they are dry and brown, about 30 minutes. Use a paring knife to cut a slit in each puff, then return them to the oven for 5 to 10 minutes to finish browning and drying. Do not let them scorch.
Step 7Remove the puffs to a wire rack and let them cool. The puffs can be prepared 8 hours in advance and stored on the wire rack at room temperature.
Step 1Cut the radishes in half and then cut them crosswise in moderately thin slices. They should be thick enough that they crunch, but not so thick they dominate the crab. Combine the sliced radishes, crab, mayonnaise, chives, tarragon and vinegar in a mixing bowl and stir to combine. Taste and add salt if necessary. You should have about 2 cups of salad. (The recipe can be made to this point and refrigerated, tightly covered, up to 8 hours in advance.)
Step 2Slice the top third off of each cream puff shell using a serrated knife. Pull out any moist dough from the center and discard (the better you dry the dough after you've added the flour, the less you'll have to throw away).
Step 3Spoon a heaping teaspoon of crab salad into the center of each shell and replace the lid. It should sit jauntily on top. Serve within an hour.