Preheat the oven to 350 degrees F. Line a 10-inch cast-iron skillet with aluminum foil and spray the foil with cooking spray.

In a large mixing bowl, stir 1 1/2 cups of the sugar into the melted butter. Beat in the eggs one at a time. Sift the flour and salt onto the batter. Add the flavoring and stir well. Pour the batter into the skillet. Top with sliced almonds and the remaining 2 tablespoons sugar. Bake until slightly brown on top, about 35 minutes. Cool the shortbread in the skillet. When cool, use the foil to lift the shortbread from the skillet; remove the foil before serving.