Drain peaches, reserving juice for the glaze. I placed my peaches between layers of paper towels while preparing the cake batter.
Combine brown sugar, flour, allspice, cinnamon, and pieces of butter in a small food chopper or processor and pulse until blended and crumbly (or cut in butter with a pastry blender). Stir in pecans. Refrigerate while preparing cake batter.
In a medium bowl, cream together butter, sugar, and vanilla. Add eggs, one at a time, beating well after each addition. In a separate bowl, combine the flour, baking powder, and baking soda. Add the dry ingredients to the butter mixture alternately with the sour cream, beginning and ending with flour. Spread batter evenly into an 8 or 9 inch square pan lightly sprayed with cooking spray.
Place peaches in an even layer on top of batter. Sprinkle with the streusel topping. Bake 30 to 40 minutes, or until toothpick inserted in the center comes out clean. Do not over bake. I used a 9 inch pan and it took exactly 35 minutes in my oven. Remove to wire rack to cool.
While the cake is cooling, prepare glaze. In a bowl, stir together melted butter, vanilla extract, and reserved peach juice. Stir in powdered sugar until a nice smooth glaze comes together. Can use more or less of the peach juice, depending on your preference for the thickness of your glaze. I drizzled a little onto my cake while it was still warm, and then drizzled on a little more when it was completely cool. I did not use all of the glaze.