With a sharp knife peel celery root and cut into 1/2-inch cubes. Thinly slice shallots and chop celery ribs.

In heavy saucepan cook vegetables in butter with salt and pepper to taste over moderately high heat, stirring, until golden, about 6 minutes. Add water and boil, uncovered, until celery root is very tender, about 15 minutes.

In a blender puree mixture in batches (use caution when blending hot liquids) until smooth, transferring to a large saucepan. Stir in lemon juice and, if necessary, more water to reach desired consistency. Season soup with salt and pepper. Keep warm.

Cut bread into cubes, or if available, use a cookie cutter to create different shapes. Heat oil in a small saute pan. Fry up croutons until golden and drain on a paper towel lined plate.

In a bowl whisk cream just until stiff peaks form.

Serve bisque topped with croutons and a dollop of whipped cream.