Preheat the oven to 350 degrees F. Place the butter in an 10-inch cast-iron skillet and transfer to the preheated oven to melt.
Meanwhile, mix together the flour, baking powder, lavender and salt in a bowl. Stir in the milk, 1 cup sugar, the lemon juice, zest and vanilla to combine. Mix together the remaining tablespoon sugar and the blueberries in another bowl. Remove the hot skillet with the melted butter from the oven and pour in the batter. Top with the sugared blueberries. Bake until brown and the batter has risen up and around the fruit, about 30 minutes.
Transfer to a rack to cool slightly. Serve with vanilla bean ice cream or lightly sweetened whipped cream.