Crust
Step 1
Whisk 1⅔ cups (208 g) all-purpose flour, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and ¼ tsp. baking powder in a large bowl. Add 2 oz. chilled cream cheese, cut into 1″ pieces, and rub into dry ingredients with your hands until incorporated (mixture will look very shaggy). Add 10 Tbsp. chilled unsalted butter, sliced ½” thick, and toss to coat in flour, then smash with your hands into smaller, flatter pieces (about chickpea-size). Make a well in the center and pour in ¼ cup ice water. Toss with a fork or your hands to distribute. Knead dough in bowl a couple times to bring together (some dry bits may remain).
Step 2
Turn dough out onto a surface lightly dusted with rice flour or all-purpose flour; dust top of dough with rice flour. Roll out to a ½”-thick rectangle. Fold in half, rotate 90°, and fold in half again. Roll out to a ½”-thick rectangle and repeat folding process, dusting with more rice flour as needed to prevent sticking. Pat dough into a ½”-thick disk; wrap tightly in plastic. Chill at least 2 hours and, preferably, up to 12 hours.
Step 3
Let dough sit at room temperature 5 minutes. Unwrap and roll out on a surface lightly dusted with rice flour to a 12″ round about ⅛” thick. Brush excess rice flour from dough and carefully transfer to a 9″-diameter pie dish, preferably metal. Lift edges and allow dough to slump down into pan, then press firmly into bottom and sides. Trim, leaving about 1″ overhang. Fold overhang underneath and press firmly to seal; crimp edges if desired. Prick bottom and sides of crust at regular intervals with a fork. Chill 15 minutes.
Step 4
Meanwhile, place a rack in lower third of oven and preheat to 375°.
Step 5
Place crust on a parchment-lined rimmed baking sheet. Line crust with 2 sheets of parchment paper (crumple parchment, then unfold so it molds to crust better) and fill with pie weights or dried beans. Bake until edges are golden brown and bottom is opaque (carefully lift parchment to check), 30–35 minutes.
Step 6
Remove crust from oven; reduce oven temperature to 325°. Lift out parchment with weights. Return crust to oven and bake until bottom and sides are evenly golden brown, 25–30 minutes. Transfer blind-baked crust to a wire rack; let cool.
Do Ahead: Dough can be made 1 month ahead; double wrap in plastic and freeze instead of chilling. Thaw overnight in refrigerator before using. Crust can be blind baked 2 days ahead; store loosely wrapped at room temperature.
Filling and Assembly
Step 7
Place a rack in lower third of oven and preheat to 375°. Cook ½ cup (1 stick) unsalted butter in a medium saucepan over medium heat, stirring often, until it foams, then browns, 5–8 minutes. Let cool 5 minutes.
Step 8
Process ⅔ cup (133 g) dark brown sugar, 2 Tbsp. all-purpose flour, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, 1 tsp. ground cinnamon, ¼ tsp. freshly grated nutmeg, and ¼ tsp. ground allspice in a food processor or blender until combined and no lumps of sugar remain. Add 3 large eggs, 1 cup well-shaken buttermilk, 2 Tbsp. dark rum, and 1 tsp. vanilla extract and process until smooth. Carefully pour in butter, scraping pan with a rubber spatula to get all the brown bits; process until combined. Scrape filling into crust.
Step 9
Bake pie until filling is set around the edges and only jiggles very slightly in the center when gently shaken, 35–45 minutes. Transfer to a wire rack and let cool at least 30 minutes.
Step 10
Dust pie generously with powdered sugar just before serving.
Do Ahead: Pie can be baked 1 day ahead. Cover and chill.