Position a rack in the lower third of the oven and preheat to 350ºF.
Combine the oats, sugars, flours, cardamom, and salt in a large bowl (or the bowl of a stand mixer fitted with the paddle attachment). Add the butter and work in with your fingers (or with the mixer on lountil the mixture begins to clump together.
Dump the crumble mixture into a 9" pie pan, and press it evenly into the sides and bottom. Freeze until firm, 15 minutes.
Bake the crust until light golden, 18-22 minutes. If the crust has slumped down the sides of the pan, press them back up with the back of a soup spoon while still piping hot. Fill the crust while hot, or let it cool. (You can wrap it and store it at room temperature for a few days or in the freezer for a month or two.)
Make the filling:
In the same bowl you used to make the crust (or the bowl of a stand mixer fitted with a paddle attachment), place the sugar, vanilla seeds, and lemon zest. Rub the mixture together between your fingers (or with the paddle on lountil the sugar is damp and the seeds are evenly distributed.
With a wooden spoon (or the paddle on low), work in the cream cheese until smooth, then slowly work in the sour cream until combined. Whisk in (or paddle on lothe lemon juice, salt, and egg until combined.
When the crust has finished baking, pour a thin layer of the custard into the bottom (about 1/4 of the mixture. Halve the apricots and lay them snugly in the shell in concentric circles, starting with the largest apricots on the outside and using the smaller ones on the inside. Pour the remaining custard over and around the apricots. Stir together the remaining 1 1/2 tablespoons of sugar and the 1/8 teaspoon of cardamom and sprinkle evenly over the top of the fruit.
Bake the pie until the custard is puffed and set and the fruit is bubbling, 25-35 minutes. Let the pie cool completely, at least 2 hours. Optionally chill for cleaner slices.
Serve the pie chilled or at room temperature. The crust is the crispest shortly after baking, but the pie will keep at room temperature for up to 1 day or chilled for up to 3 days.
Adapted from The Four and Twenty Blackbirds Pie Book.Feel free to trade the apricots here for the fruit of your choice; peaches, nectarines, cherries, figs, or berries would all work well.If gluten isn't an issue for you or your guests, trade the flours in the crust for all-purpose wheat flour. If gluten is an issue, be sure to source oats and oat flour that are certified gluten-free. (I get mine from GlutenFreeOats.com.)To quickly warm your cream cheese to room temperature, cut it into cubes and place it in a bowl near the oven while you make the crust.All ounce measurements here are by weight.Nutritional values are based on one of eight servings.