Center a rack in the oven and preheat the oven to 350 degrees F.
Butter a 9 inch cast iron skillet or a 9 inch cake pan or have used a pie pan.
In a medium bowl, pour the sugar. Add the zest and blend the zest and sugar together with your fingertips until the sugar is moist and aromatic.
Whisk in the eggs one at a time until well blended. Mix in the salt and the extracts.
Stir in the flour.
Fold in the melted butter. Scrape the batter into the pan and smooth the top. Evenly sprinkle the sliced almonds over the top and sprinkle evenly with sugar.
If you're using a cake or pie pan, place the pan on a baking sheet.
Bake the cake for 25 to 30 minutes, or until it is golden and a little crisp on the outside.
Remove the pan from the oven and let the cake cool for 5 minutes, can run a thin knife around the sides and bottom of the cake to loosen it, or serve straight from the skillet.
Sprinkle with confectioners' sugar if desired.