1. Preheat the oven to 350°F and line a 9×13-inch baking pan with parchment paper or grease it lightly.

2. In a large bowl, cream the softened butter and granulated sugar until light and fluffy.

3. Beat in the eggs one at a time, then mix in the vanilla extract.

4. In a separate bowl, whisk together 2 cups of the flour, baking powder, and salt.

5. Gradually add the dry ingredients to the wet mixture and stir until a soft dough forms.

6. Press about two-thirds of the dough evenly into the prepared pan.

7. In another bowl, toss the diced peaches with cornstarch, lemon juice, cinnamon, and nutmeg.

8. Spread the peach mixture evenly over the dough layer.

9. In a small bowl, combine the remaining 1/2 cup flour, brown sugar, oats, and melted butter until crumbly.

10. Tear the remaining dough over the peach layer, then sprinkle the streusel mixture evenly on top.

11. Bake for 38 to 45 minutes, until the top is lightly golden and the fruit is bubbling near the edges.

12. Cool completely before slicing into bars.