Spray a 9 inch round cake pan with 2 inch sides with non-stick spray
In a small saucepan melt 4 tablespoons of the butter with the brown sugar, and stir until sugar is dissolved. Pour into bottom of prepared cake pan.
Arrange peach slices in a circular pattern in one layer over the brown sugar mixture. Arrange blueberries in the centre if you are using them.
Add remaining 8 tbsp (half cup) butter and the granulated sugar to the bowl of electric mixer and beat until light and fluffy.
Add eggs one at a time, beating well after each addition. Add vanilla and beat until combined.
In a large bowl sift together the flour, baking powder, salt and spices.
Add 1/4 cup milk and half of the flour mixture to the bowl and beat until combined. Add final remaining milk and flour mixture and beat for 1 to 2 minutes.
Carefully pour batter over top of the peaches and gently spread to cover peaches completely. Smooth with a spatula
Bake at 350 degrees for 40 to 50 minutes, or until toothpick comes out clean.
Notes
If you don't have a 9 inch cake pan with high sides, simply use a regular cake pan, filling about 3/4 full and then use the remaining batter to make cupcakes. Reduce bake time of cake to 30 to 35 minutes, testing with a toothpick to come out clean.