In an enamel-coated cast-iron grill pan, melt butter over medium heat. Cook doughnuts, carefully turning with a spatula, until grill marks form and doughnuts are heated through, about 2 minutes per side.
Layer 2 doughnuts each with ½ cup whipped cream and 2 tablespoons blueberries; repeat layers. Sprinkle with confectioners’ sugar and lemon zest; serve immediately.
Recipe by Southern Cast Iron at https://southerncastiron.com/grilled-doughnut-stacks/