How to Make It
Preheat the oven to 400°. In a small saucepan of boiling salted water, cook the chestnuts until just tender, about 5 minutes. Take 1 chestnut out of the water at a time and while still hot, hold it with a kitchen towel and peel with a paring knife. Crumble the chestnuts.
In a small saucepan, cover the chestnuts and celery root with the 1 1/2 cups of water and the cream, add a pinch of salt and bring to a boil. Simmer over moderate heat until the celery root is very tender, about 25 minutes. Transfer the mixture to a blender and puree until silky. Pour the soup into a small saucepan and season with salt and white pepper.
Brush the baguette slices with olive oil and bake until crisp, about 5 minutes. In a small skillet, heat the 1 teaspoon of olive oil. Add the chorizo and cook over moderate heat until sizzling, about 1 minute.
Remove the small white muscle from the side of each scallop. Slice the scallops crosswise 1/8 inch thick. Arrange the scallop slices on the bottom of 4 shallow bowls and season with salt and pepper. Scatter half of the chorizo on top. Bring the soup to a simmer and pour it over the scallops. Top with the remaining chorizo and serve right away, with the baguette toasts.