Popcorn Sandwich Cookies with Salted Caramel Recipe

Ingredients

• 1 stick (4 ounces) unsalted butter, at room temperature
• 1 cup sugar
• 1 large egg
• 1 cup all-purpose flour
• 1/3 cup cornstarch
• 1 teaspoon baking powder
• 1/2 teaspoon kosher salt
• 3 cups popped unsalted popcorn, very coarsely ground in a food processor
• 1 1/3 cups sugar
• 1/2 cup heavy cream
• 1 tablespoon coarse sea salt