Chunky Apple Muffins

INGREDIENTS

• Vegetable cooking spray
• 1 medium Granny Smith apple, peeled, cored, and quartered
• 1 cup sugar
• 2 cups all-purpose flour
• 2 teaspoons baking soda
• 1/2 teaspoon plus 2 pinches salt
• 1/2 teaspoon ground cinnamon
• 1/4 cup chopped walnuts, toasted (omit if serving to children under 3)
• 2 large eggs
• 1 cup buttermilk, room temperature
• 1/2 cup (1 stick) unsalted butter, melted