Rhubarb Buckle - The Kitchen at Middleground Farms

Ingredients

• 4 tablespoons butter, divided
• 1 ½ pounds rhubarb, trimmed and cut ½ inch thick on the bias
• 1 cup sugar
• 1 teaspoon cornstarch
• 2 cups all-purpose flour
• 1 ¼ teaspoons baking powder
• 1 teaspoon coarse salt
• 1 ½ sticks unsalted butter, softened
• 1 cup sugar
• 1 teaspoon finely grated lemon zest
• 3 large eggs
• 1 teaspoon pure vanilla extract
• ½ cup sour cream or yogurt
• Crumb Topping
• 1 cup all-purpose flour
• ¼ cup light-brown sugar
• ¼ teaspoon coarse salt
• ½ stick unsalted butter, melted