To begin, preheat oven to 325 degrees.
Over medium high heat, coat a small sauté pan with grape seed oil. Add curry powder and allow the spice to release its color and essential oils (approximately 30 seconds). Add one cup of the chopped cauliflower florets to the curry oil and toss to coat. Place the pan in the oven and roast briefly (three to five minutes). Remove from oven and reserve at room temperature.
In a heavy-bottomed pot, sweat leeks in olive oil. Add cream, remaining cauliflower florets, and enough vegetable stock or water to cover. Gently simmer until cauliflower has completely softened (approximately 20 minutes). Purée with an immersion blender until smooth. Strain purée and season with salt and Champagne vinegar to taste. Reserve hot or chill.
To serve has an hors d’oeuvre, fill small ramekins one-half full with purée, garnish with a generous portion of caviar, curried florets and a sliced scallion. To serve as a soup, quadruple recipe, follow the same instructions and serve in bowls.