Plum Cornmeal Upside-Down Cake

Ingredients

• 8 Tbsp. (1 stick) unsalted butter, melted, divided
• 1/3 cup brown sugar, packed
• 1 pound plums, halved, pitted
• 1/4 tsp. ground cinnamon
• Pinch of sea salt
• 1 cup all-purpose flour
• 1/2 cup cornmeal
• 1 tsp. baking powder
• 1/2 tsp. sea salt
• 1/8 tsp. baking soda
• 3/4 cup granulated sugar
• 1/2 cup milk (whole milk or coconut milk recommended)
• 2 eggs
• 1/4 cup fresh-squeezed lemon juice
• 2 tsp. lemon zest