Serve chilled with potato or bagel chips.
1 medium onion, sliced 1/3 inch thick
3 or 4 shallots, sliced 1/3 inch thick
¾ cup sour cream
¼ cup grated Pecorino Romano or Parmesan cheese
½ teaspoon salt, or more to taste
Fire up a gas or charcoal grill, bringing the temperature to medium low.
Coat the onion and shallot slices with oil. Place on a small mesh grill rack or in a grill wok.
Grill uncovered over medium-low heat for 18 to 20 minutes, turning several times. The onion and shallots are ready when they are very soft with lightly charred edges. They can be grilled a day ahead.
Purée the onion and shallots in a food processor, then add the remaining ingredients and continue processing until nearly smooth. Chill the dip for at least 30 minutes.
Makes about 2 cups.