Preheat oven to 350°F. Pour melted butter into an 8-inch square baking pan.
In a small bowl, combine cherries with 1 Tbsp. flour and 1/2 cup sugar. Mix until ingredients are well incorporated.
In a large bowl, mix together baking powder and remaining flour and sugar. Stirring constantly, gradually add milk to mixture and combine to form a thin batter. Stir in vanilla and salt.
Pour batter into pan over melted butter; spread out evenly. (Do not mix butter and batter together.) Spread cherry mixture evenly over batter. Bake until cake is golden brown on top and just firm to the touch, about 45 minutes.