In a small bowl, stir together the cornstarch and cold water until the slurry runs smooth. Set aside.
Add the peach puree, brown sugar, lemon juice, vanilla extract, cinnamon, and nutmeg to a 3 qt saucepan. Stir to combine the ingredients.
Bring the peach mixture to a simmer over medium heat, stirring frequently.
Once simmering, lower heat to medium-low or low. Whisking constantly, add the cornstarch slurry to the pot in a slow steady drizzle.
Cook for an additional 2-3 minutes, stirring constantly, until the jam thickens. The mixture should release large bubbles and make a rustling noise when it’s stirred.
Remove the pot from heat and allow the jam to cool completely. Placing the mixture in the fridge will speed up the process.
For the Cinnamon Streusel
Add all ingredients to a medium sized bowl and mix with your hands or a fork until crumbly.
This mixture may be prepared a few hours before.
For the Cake Batter
Sift together the flour, baking soda, and salt into a bowl. Set the bowl aside.
In your stand mixer bowl, beat the butter and sugar together on high speed for 3-4 minutes, or until very pale yellow and fluffy.
Next add eggs, one at a time, combining well after each addition and scraping down the sides of your bowl as needed. Add the vanilla extract with the final egg.
Turn your mixer down to its lowest speed, and slowly add half of the flour to batter. Blend on low speed just until the flour is mixed in. Stop the mixer and scrape down the bowl and beater.
Add the sour cream to the bowl and blend on low speed until it’s just blended in. Scrape down sides and and beater again.
Finally, add the remaining flour. Mix until just combined, then scrape down the bowl and beater one last time.
Mix for 30 seconds on low and turn off the mixer.
Preheat your oven to 350F then liberally grease or spray a 14 or 15 cup bundt pan with non stick baking spray.
Sprinkle ⅓ of the cinnamon streusel into the bottom of the pan.
Cover the streusel with ½ of the cake batter. Make a well, then sprinkle ⅓ of the cinnamon streusel into the well.
Pour remaining cake batter over the streusel. Make a shallow well in the batter.
Spoon the peach jam on top of the batter. Sprinkle the remaining streusel over the jam.
Gently tap the pan against the countertop, then bake the cake for 1 hour to 1 hour 15 minutes, or until a toothpick inserted in the center of the cake comes out clean. *Darker pans may bake the cake faster than lighter colored pans will.
Cool in pan on a wire rack for 10 minutes then invert cake on a serving plate for at least an hour or until the cake is cool to touch. Allow the cake to cool completely to prevent the peach jam from oozing out when you cut it.
For the Maple Glaze
Once the cake is completely cooled, whisk together the confectioner's sugar, maple syrup and milk. Add more milk or syrup if needed. Glaze should be pourable but not too thin.
Drizzle glaze over cooled cake and serve.
The creaming period of butter and sugar is crucial for adding an amazing texture to your cake so don't try to hurry through this. Also make sure you don't over beat when you add the flour since it begins producing gluten.