Plum snack cake with Pecan Topping

Ingredients

• ¼ cup packed light brown sugar
• ¼ cup all-purpose flour
• 2 tablespoons unsalted butter (¼ stick), plus more for coating the pan
• ½ teaspoon ground cinnamon
• Pinch fine salt
• ½ cup finely chopped pecans
• 1 ¼ cups all-purpose flour
• 1 teaspoon baking powder
• ¼ teaspoon salt
• 1/3 cup whole milk
• 1 teaspoon vanilla extract
• ¾ cup sugar
• 6 tablespoons unsalted butter at room temperature
• 2 eggs, at room temperature
• 5 medium plums, pitted and cut into ¾ -inch pieces