Rosemary, Caramelized Onion, & Potato Galette

Ingredients

• 1 tablespoon minced garlic
• Heavy cream or egg for the crust
• ¼ cup finely grated Parmesan or Asiago cheese
• ⅓ cup ice water
• 2 tablespoons olive oil
• 1 tablespoon neutral oil
• ½ teaspoon salt
• 1 tablespoon butter
• 3-4 ounces Parmesan or Asiago cheese, finely grated , plus more if desired
• 2 tablespoons minced rosemary
• ½ teaspoon sea salt or kosher salt
• 1 ¼ cups all-purpose flour
• 1 stick unsalted butter, frozen or nearly frozen
• Salt and black pepper
• 2 medium onions, any color, sliced into half-moons
• ½ pound Yukon Gold potatoes
• 2-3 tablespoons balsamic vinegar