In a large bowl, mix cake batter as directed on box. For a more rustic cake, you can leave it a bit clumpy. (This is one point where you could add extract)
In a small bowl, mix brown sugar and corn starch until well combined
In a small nonstick skillet, heat peaches in juice, breaking them up a little. (You can also add the extract here if you choose to use it.) Add the brown sugar mixture and stir until thickened.
In an ungreased 9x13 cake pan (I use Pyrex, which comes with a lid for storage and transport) pour cake batter. Drop peaches by large spoonfuls all over the batter. (If you want almonds, sprinkle them on at this point.)
Bake at 350 degrees for 25-35 minutes. Don't over-bake; it's best when it's still a little gooey.
Serve hot or cold, with ice cream or milk, or sneak spoonfuls from the pan every time you pass the kitchen. ;)