Prep the produce: Dice the onion and mince the garlic. Quarter the radishes and slice a few thinly for garnish.
Peel and dice the potato. Rinse and pat dry your edible flowers and herbs.
Sweat the aromatics: Warm the butter and olive oil in a medium pot over medium heat. Add onion and a pinch of salt.
Cook 5–7 minutes, stirring, until translucent and soft. Add garlic and cook 30 seconds, just until fragrant.
Add vegetables and simmer: Stir in the radishes and potato. Season with 1/2 teaspoon salt and a few grinds of pepper.
Pour in the broth. Bring to a boil, then reduce to a gentle simmer. Cook 15–18 minutes, until potatoes are tender and radishes are soft.
Blend until silky: Turn off the heat.
Use an immersion blender to puree until smooth, or blend in batches in a countertop blender. For extra silkiness, blend 30 seconds longer than you think you need.
Finish and brighten: Return the soup to low heat if needed. Stir in cream or whisk in yogurt.
Add lemon zest and juice. Taste and adjust with more salt, pepper, or lemon to balance the richness.
Garnish like a pro: Ladle into warm bowls. Top with a few thin radish slices for crunch, a sprinkle of chopped herbs, and a scattering of edible petals.
Finish with a light drizzle of extra-virgin olive oil. Serve immediately.