Pumpkin Chocolate Chip Muffins

Name: Pumpkin Chocolate Chip Muffins
Ingredients: Unsalted butter , for greasing muffin pan, optional; 2 cups ( 240 g ) all-purpose flour , plus more for muffin pan; 1 tablespoon pumpkin pie spice; 1 1/2 teaspoons baking powder; 1/2 teaspoon baking soda; 1/2 teaspoon kosher salt; 1 ( 15 - ounce ) can pumpkin puree; 1 1/4 cups ( 270 g ) light brown sugar , packed; 2 large eggs; 1/2 cup vegetable oil; 1 cup ( 170 g ) semi-sweet chocolate chips