Makes 24 endive Spears, serves 6 to 8.
In a medium bowl, gently mix together the crab, fennel, mayonnaise, yogurt, shallot, tarragon, chile pepper, lemon zest, breaking up any large claw meat pieces with a fork. Season to taste with salt and white pepper. (The filling can be made up to 4 hours in advance. Store in an airtight container in the refrigerator until ready to use.)
Immediately before serving, slice about 1Ž4-inch off the base of each endive and separate the leaves; you will need 20 large leaves; the remaining smaller leaves can be uses in salads. Fill the concave part of each leaf with a scant tablespoon of the crab mixture and arrange them on a long serving platter.