Preheat your oven to 180°C (350°F).
In a small saucepan, melt 1/4 cup (60g) of butter and stir in the brown sugar until dissolved. Pour this mixture into the bottom of your cake pan and arrange the peach slices on top.
In a mixing bowl, whisk together the flour, baking powder, and salt. In another bowl, beat the remaining butter and granulated sugar until light and fluffy. Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.
Gradually add the flour mixture to the butter mixture, alternating with the milk, and mix until just combined.
Pour the batter over the peach slices in the cake pan, spreading it evenly.
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes, then carefully invert it onto a serving plate. Serve warm or at room temperature.