Add the onion, carrot, celery, parsley stems, bay leaf, and peppercorn and return to a boil.
Cover and immediately remove from heat.
Leave covered and let steep for 30 to 40 minutes, then strain and reserve liquid, discarding the solids.
Bring the vegetable stock to a gentle simmer in a medium-sized pot. Blanch the parsley tops in the stock for 10 seconds, then transfer them to a bowl of ice water to stop the cooking. Reserve the vegetable stock over the heat. Drain and reserve the parsley separately.
In a second pot, warm the butter over medium heat, then add the garlic and onion. Cook for three minutes, until starting to soften.
Stir the potato into the onion then deglaze with the white wine. Bring to a simmer and reduce by half, about five minutes.
Combine the warm vegetable stock with the onion-potato-wine mixture, bring to a simmer and cook for one hour.
Add the reserved blanched parsley and horseradish and blend until smooth.
Return to medium-low heat, whisk in crème Fraiche and keep warm until ready to serve.
Toss radish, shallot, parsley, olive oil, and lemon juice together in a small mixing bowl. Season with salt and pepper and reserve for plating.
Pre-heat oven to 375° F (190° C).
Toss the baguette pieces with melted butter, salt, and pepper.
Spread on a baking sheet, and bake for 8-10 minutes, until golden brown.