Preheat your oven to 180 degrees celsius (350 degrees Fahrenheit).
Wash and cut 3-4 nectarines into wedges or slices. Set aside and make the batter.
Mix the butter(room temperature) and sugar using the paddle attachment and beat at a moderate speed (3-4 on a stand mixer)until mixture is light and fluffy (about 3 minutes). Note: A hand mixer can be used.
Add the eggs (room temperature) and the vanilla and beat at medium speed until mixture is smooth. Note: Scrape the side and bottom of bowl regularly to ensure thorough mixing of ingredients.
Add milk and sour cream and beat at low speed until just combined.
Prepare the flour. In a separate bowl, mix flour, baking powder and salt with a fork. Sift the flour mixture on top of the wet ingredients in the stand mixer. Turn the mixer on low and stop as soon as batter comes together. Be careful not to overmix. Using a spatula, carefully scrape the side and bottom to incorporate the ingredients.
Grease a cake tin with a tablespoon of butter and gently place the batter into the tin. Level the batter with a spatula or offset spatula. Place the peaches on top of the batter.
Make the streusel. In a bowl, mix the flour, sugar and cinnamon together and then add the butter. Mix everything until the mixture becomes crumbly.
Sprinkle the streusel mixture over the cake and the peaches, making sure it is spread evenly throughout the cake.
Bake the cake at 180 degrees Celsius for 45-50 minutes. When a toothpick through the centre of the cake comes out clean, it is ready. Note: If the streusel starts turning very dark, place tinfoil over the cake while baking to stop the colour changing further.
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.