Romano Risotto with Radishes

Ingredients

• For risotto:
• 6 cups chicken or vegetable broth
• 2 cups hot water
• 3/4 stick unsalted butter (, divided)
• 1 medium onion (, finely chopped (1 cup))
• 3 garlic cloves (, finely chopped)
• 1 pound Arborio rice ((2 1/2 cups))
• 2/3 cup dry white wine
• 1/2 cup Pecorino Romano or Parmiggian cheese (, grated)
• For radishes:
• 1 tablespoon white-wine vinegar
• 1 tablespoon extra-virgin olive oil
• 1 pound trimmed radishes (, julienned)
• 1 tablespoon finely chopped green onion
• Accompaniment: extra-virgin olive oil for drizzling