Preheat your oven to 325°F (165°C). Generously grease and flour a 10 or 12-cup Bundt pan, making sure to get into all the crevices. Set aside.

In a small bowl, whisk together the all-purpose flour, brown sugar, granulated sugar, and cinnamon. Add the cold, cubed butter. Using a pastry blender or your fingertips, cut the butter into the mixture until it resembles coarse, crumbly sand. Place the streusel in the refrigerator to keep cold while you prepare the rest of the recipe.

In a medium bowl, gently toss the diced peaches with the brown sugar, cornstarch, cinnamon, nutmeg, and lemon juice until the peaches are evenly coated. Set aside.

In a separate medium bowl, whisk together the 3 cups of all-purpose flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the softened butter and cream cheese on medium-high speed until smooth and creamy, about 2 minutes.

Gradually add the granulated sugar and continue to beat on medium-high speed for 5-7 minutes, until the mixture is very light, pale, and fluffy. Scrape down the sides and bottom of the bowl as needed.

Add the eggs one at a time, beating well after each addition and scraping down the bowl. Once all eggs are incorporated, beat in the vanilla extract.

Reduce the mixer speed to low and add the dry ingredients in three additions, mixing only until just combined. Do not overmix.

Spoon about one-third of the pound cake batter into the prepared Bundt pan and spread it evenly.

Carefully spoon half of the peach filling (including juices) over the batter. Sprinkle with half of the chilled streusel.

Add another third of the cake batter, spreading gently to cover the filling. Top with the remaining peach filling and the remaining streusel.

Spoon the final third of the batter over the top and gently spread to cover the filling layer completely. Tap the pan on the counter a few times to settle the batter and remove any large air bubbles.

Bake for 70-80 minutes, or until a long wooden skewer inserted into the center of the cake comes out with moist crumbs attached, but no wet batter. If the top begins to brown too quickly, you can loosely tent it with aluminum foil.

Let the cake cool in the Bundt pan on a wire rack for exactly 15 minutes. This is a critical step to ensure it releases cleanly. After 15 minutes, carefully invert the cake onto the wire rack to cool completely.

Once the cake is completely cool, prepare the glaze. In a small bowl, whisk together the sifted powdered sugar, 2 tablespoons of milk, and the vanilla extract until smooth. If the glaze is too thick, add more milk, a half teaspoon at a time. Drizzle the glaze over the cooled cake and let it set before slicing and serving.