Preheat the oven to 375°F.
Butter and flour a 10-inch angel food cake or Bundt pan
Whisk together the flour, baking soda, and salt in a medium bowl. Set aside.
Using a mixer, cream the butter and sugar until light and fluffy, about 3-5 minutes. Beat in the eggs one at a time, then add the sour cream and vanilla, mixing until thoroughly combined.
Gradually add the flour mixture to the butter and sugar mixture, mixing until the dry ingredients are fully incorporated.
Pat the peach slices dry with a paper towel to reduce excess moisture. Toss them with 2 tablespoons of flour and gently fold them into the cake batter.
Spoon about half of the batter into the prepared pan. Sprinkle a generous layer of streusel crumble over the batter. Spoon the remaining batter over the streusel layer and smooth the top with the back of a spoon.
Place the cake in the oven and immediately reduce the temperature to 350°F. Bake for 45 minutes.
While the cake is baking, slice the remaining peach into 8-10 slices, sprinkle them with the juice of ½ a lemon, and set aside.
After 45 minutes of baking, the cake should begin to brown. Carefully open the oven and gently pull out the oven rack slightly to arrange the peach slices on top of the cake. Be cautious not to move the cake too much, as this may cause it to fall.
After arranging the peach slices, slide the cake back into the oven, reduce the temperature to 325°F, and bake for an additional 45 minutes. If the top of the cake begins to brown too quickly, cover it with foil.
Remove the cake from the oven and let it cool completely on a rack before removing it from the pan.
To remove the cake from the pan, place a plate or rack over the top of the pan, then flip the pan over while holding the plate/rack in place. The cake should release easily. Flip the cake right side up onto another plate.
Microwave the jam for a few seconds and brush it over the peach slices to give them a glossy finish.