Upside Down Pear Skillet Cake

Name: Upside Down Pear Skillet Cake
Prep time: 25 min
Cook time: 45 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 4 Tablespoons butter; ½ cup brown sugar (packed ); ¼ cup maple syrup; 2 large pears (I used Bosc - peel, core and slice into approx 1/4-inch thick slices); 1 cup walnut pieces (lightly toasted); 1 and ½ cups all-purpose flour; 1 and ½ teaspoons ground cinnamon; 1 teaspoon baking soda; ½ teaspoon salt; ½ cup Greek yogurt; ½ teaspoon pure vanilla extract; ½ teaspoon black walnut extract; ½ cup butter (at room temperature); ½ cup granulated sugar; ⅓ cup maple syrup; 2 large eggs (room temperature)