Preheat the oven to 350F (180C).
Sift the flour into a mixing bowl, then add the brown sugar, baking powder and mix.
Add all the other ingredients, except peaches and whisk together.
Remove the pits from the peaches. Cut 3 of them into small cubes and the other 3 in slices.
Add the cubed peaches to the batter and mix.
Grease a tin (I used a rectangular, ~30cm long, pound cake tin).
Pour the mixture in and top with the sliced peaches. Sprinkle some brown sugar on top.
Bake for 25 minutes. Test with a toothpick. Insert it in the middle of the peach sponge cake and if it comes out clean, it's ready. Otherwise, let it bake for a couple more minutes.
Let it cool before serving. I didn't wait, so that's why it may look a bit too fragile in the photos, but trust me, when it's cool, it's just perfect!