Preheat oven to 350°. Place the butter in an 8” x 8” square pan and put it in the oven to melt as the oven preheats.
In a medium bowl, sift the flour; baking powder and salt, and then mix in ¾ cup sugar Fold in the milk and vanilla, stirring just until everything’s moistened.
Slice the peaches and toss gently with the remaining ¾ cup sugar (or more, depending on sweetness), nutmeg and lemon juice in a second, larger bowl.
Remove the pan with the melted butter from the oven and pour the batter mixture over the melted butter Do not mix. Carefully place the peaches on top of the batter; do not stir
Bake until golden brown and puffy, about 45–55 minutes.