Italian plum cake recipe

Ingredients

• 1/2 cup butter, room temperature
• 1/2 cup granulated sugar
• 1 egg
• 1 cup unbleached all-purpose flour
• 1/2 teaspoon baking powder
• 1/4 cup milk
• 1/2 teaspoon vanilla extract
• pinch of salt
• 10 - 12 Italian plums
• Topping
• 1/4 cup butter
• 1 cup granulated sugar
• zest of 1 lemon
• 1 tablespoon fresh lemon juice