Sour Cream-Apple Pie with Lemon-Cardamom Streusel

My mom and I swooned over this pie via email a few months ago, and just had to make it once I got home, even thought it was the middle of summer!  Despite the hot weather, this apple pie was a huge hit.  The original recipe is for a huge deep dish pie, but we halved everything except the crust and it still made plenty (and fit in a regular pie plate).  We had some homemade apple pie filling from one of my mom's students, so we subbed that for the apples in the original pie and just added some egg, sour cream, and lemon zest to mimic the original filling - this worked really well, but I've listed the original filling recipe below in case you don't have a jar of homemade filling around the house!  Feel free to add some cinnamon if you like - although the original recipe doesn't list it, the filling we used already had some mixed in and it was very tasty. 

Sour Cream-Apple Pie with Lemon-Cardamom Streusel (adapted from Unforgettable Desserts)

For the crust:
1/2 cup unsalted butter, at cool room temperature, cut into small pieces
5 tablespoons sugar
1 large egg yolk
1 1/4 cups sifted cake flour

For the apple filling:
4-1/2 cups peeled, cored and thinly sliced apples (about 5 apples)
1/3 cup sugar
3 tablespoons all-purpose flour
1 large egg, at room temperature
1 cup sour cream (not low-fat)
1 teaspoon finely grated lemon zest

For the streusel:
1/2 cup all-purpose flour
1/4 cup (4 T) unsalted butter, melted
1/4 cup firmly packed light brown sugar
1 teaspoon finely grated lemon zest
1/4 teaspoon ground cardamom

Make the crust:
1. In the bowl of a stand mixer, beat the butter with the flat paddle attachment on medium-high speed until creamy, about 1 minute. Add the sugar slowly and continue to beat on medium-high speed until lightened and creamy, about 2 minutes. Beat in the egg yolk until well combined. Add the flour and pulse the mixer on and off until it begins to combine, and then run the mixer on medium-low speed just until the dough begins to form. Scrape out onto plastic wrap and press the dough into a flat disk. Wrap and chill for at least 2 hours or overnight.
2. Roll out the dough on a lightly floured surface until large enough to fit in your pie plate - a deep dish pie plate is best here. Fit the dough into the pan, trim the edges, and crimp edges with a fork.  Chill for at least 2 hours or overnight.

Make the filling:
1. Position a rack in the middle of the oven. Preheat the oven to 400 degrees.
2. Toss together the apple slices and sugar in a large sauté pan. Cook over medium heat, occasionally stirring gently. Cook for about 5 minutes, just until the apples soften just a bit. Remove from the heat, cool slightly, then sprinkle with flour and toss gently to coat.
3. Whisk the eggs in a large bowl, then whisk in the sour cream and lemon zest. Fold into the apples.
4. Remove the crust from the refrigerator and scrape the filling into the crust.  Bake for 15 minutes while you prepare the streusel.


Make the streusel:
1. Combine all the ingredients until well blended.
2. After the pie has baked for 15 minutes, remove from the oven and turn the heat down to 375 degrees. Scatter the streusel over the pie, forming it into small clumps with your fingers.
3. Return the pie to the oven and bake for 15 minutes more. Turn the heat down to 350 degrees and continue baking for 20 to 30 minutes more, or until the streusel is evenly browned. If the crust is getting to brown, cover it with foil. 
4. Cool the pan on a rack to allow the filling to thicken and set. Serve at room temperature.