Rhubarb crumb bars

Ingredients

• 6 tablespoons unsalted butter, melted, plus room-temperature butter for pan
• 1 cup all-purpose flour (spooned and leveled), plus more for pan
• 1/2 cup packed light-brown sugar
• 1/4 teaspoon salt
• 1 pound rhubarb, cut into 1/2-inch pieces
• 1 tablespoon light-brown sugar
• 1 cup all-purpose flour (spooned and leveled)
• 1/2 teaspoon baking powder
• 1/2 cup (1 stick) unsalted butter, room temperature
• 1 cup confectioners' sugar
• 2 large eggs
• 1/2 teaspoon pure vanilla extract
• recipeIngredient ends