INGREDIENTS
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1 cup (2 sticks) unsalted butter, softened
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1 3/4 cup granulated sugar
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2 lemons, zested
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3 eggs
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1 tsp pure vanilla extract
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2 1/2 cups + 2 tbsp all-purpose flour, divided
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1 tsp baking powder
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1 tsp Kosher salt
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3/4 cup buttermilk
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3 cups rhubarb, diced in 1/2-inch pieces
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2 cups icing sugar
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1 lemon, juiced
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1 tbsp melted unsalted butter