To make the filling, stir together peaches, sugar, flour, cinnamon, and nutmeg. Set aside while you prepare the bars. If your peaches are juicy, pour off accumulated juices before you add in the sugar, flour, etc.
To make the bars, beat together butter and sugar, until light in color and well-combined.
Stir in eggs, one at a time, beating well after each addition.
Add in vanilla extract, and stir until combined.
Add the flour, baking powder, and salt; mix until just incorporated.
Add three-fourths of the dough mixture into the prepared pan, smoothing as needed.
Pour the peaches evenly over the dough.
Drop the remaining dough evenly over the peaches, and spread until it covers most of the peach filling.
Bake for about 25-35 minutes, or until golden brown.