This is a lightly sweetened cake that allows the fresh flavor of the peaches to shine through. If you like your desserts sugary (like my daughter does), feel free to increase the amount of sugar that goes into the skillet by up to double. The same goes if your peaches are not quite sweet enough. But my husband and I like it just like this.
Combine the dry ingredients in a medium-sized mixing bowl. Combine the soy milk, vanilla, and lemon zest in a separate bowl. Set aside without mixing them together.
Combine the peaches with the 2 tablespoons of sugar. Wipe or spray a 10-inch, well-seasoned cast iron skillet with oil. (This step is very important if you want to be able to get the cake out of the pan.) Begin heating it and add the 1/4 cup (or more) of sugar and the 2 tablespoons water. Heat and stir until the sugar is completely melted. Continue to cook and stir until the mixture is bubbly and slightly reduced (but be careful not to burn it). Place the peaches on top of the sugar and remove from heat:
Add the liquid ingredients to the flour mixture, stirring briefly just to moisten. Pour and smooth the batter over the peaches, covering them entirely. Put the skillet into the oven (you may want to place a cookie sheet or foil on the shelf below it to catch drips) and bake until the sides of the cake pull away from the edges of the pan and a toothpick comes out clean (about 30-40 minutes):
Allow the cake to cool in the pan for about 15-30 minutes. Then, run a knife around the edges of the cake to loosen it from the pan. Place a large plate or serving platter over the top and invert the skillet. Remove the skillet carefully from the cake:
Be sure to scrape any caramelized juices from the pan and smooth them over the peaches. Voilà! Peach Upside-Down Cake!
Serve warm or at room temperature, alone or with vanilla non-dairy ice cream. Makes about 8 servings.