Finely grate zest from 1 large orange into a small bowl; cover and set aside. Halve orange and squeeze juice into a measuring glass (you should have about ¼ cup); set aside.

Cook 8 oz. fresh or frozen cranberries, ¾ cup (150 g) sugar, and ¼ cup water in a medium saucepan over medium-high heat, stirring often, until sugar is dissolved and cranberries are coated in syrup but still intact, 5–7 minutes. Using a slotted spoon, transfer about ¼ cup cranberries to a wire rack; let sit until dried slightly and tacky, about 10 minutes.

Place remaining ⅓ cup (67 g) sugar in a small bowl. Add cranberries and toss to coat evenly; set aside in sugar.

Add 1 Tbsp. unsalted butter, 2 tsp. vanilla bean paste or vanilla extract, ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt, and reserved orange juice to remaining cranberries in pan. Cook, stirring often, until cranberries burst, juices are syrupy, and pan is visible when a spoon is dragged across the bottom, 12–15 minutes. Let cool, then transfer to a large measuring glass and blend with an immersion blender to make a coarse jam. (Or, use a regular blender.) Do Ahead: Sugared cranberries and jam can be made 6 hours ahead. Store separately, covered, at room temperature.

Place a rack in middle of oven; preheat to 325°. Lightly coat two 8"-diameter cake pans with nonstick vegetable oil spray or unsalted butter, room temperature; line bottoms with parchment paper rounds. Mix 2 cups plus 3 Tbsp. (250 g) bleached cake flour, 1½ cups (300 g) sugar, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, 1½ tsp. baking powder, and ½ tsp. baking soda in the bowl of a stand mixer fitted with the paddle attachment on low speed to combine, about 1 minute.

Add ½ cup vegetable oil and 6 Tbsp. (¾ stick) unsalted butter, room temperature, increase speed to medium-low, and beat until a thick paste forms (it should resemble wet sand), about 1 minute. Add 1 cup buttermilk, 2 tsp. vanilla bean paste or vanilla extract, and reserved orange zest; beat until pale and fluffy, about 2 minutes (this mixing time will help keep the cake from sinking later; don’t worry about overmixing).

Add 3 large eggs one at a time, beating 30 seconds after each addition; batter should be smooth and creamy. Divide between prepared pans; smooth surface.

Bake cakes until a wooden tester inserted into the centers comes out with only a few moist crumbs attached, 30–35 minutes. Transfer pans to a wire rack; let cakes cool in pans 15 minutes. Run an offset spatula or small knife around sides of cakes to loosen; turn out onto rack (leave parchment). Let cakes cool completely. Do Ahead: Cakes can be baked 1 day ahead. Store tightly wrapped at room temperature.

Heat 12 oz. white chocolate, coarsely chopped, in a heatproof bowl set over a saucepan of barely simmering water (bowl should not touch water), stirring, until melted and smooth. Remove bowl from heat and let white chocolate cool until barely lukewarm but still fluid.

Beat 8 oz. cream cheese, room temperature, 10 Tbsp. unsalted butter, room temperature, and a large pinch of kosher salt in the clean bowl of stand mixer fitted with the paddle attachment on medium speed until light and creamy, 8–10 minutes. Reduce speed to low and, working in 2–3 batches, add white chocolate, beating to combine after each addition. (If chocolate is too warm, frosting may be soupy. Chill until it’s cold around the edges, then beat until smooth.)

Remove parchment paper from cakes; discard. Place a cake, right side up, on a cake stand or large plate (a cake turntable works great). Transfer 1 cup frosting to pastry bag fitted with tip. Pipe a border of frosting along top edges of cake. Spread 1 cup cranberry jam over surface within frosting border. Place second cake, upside down, on top. Spread top and sides of cake with remaining frosting in bowl. Pipe a ring of frosting around top edges of cake and fill in surface with remaining jam. Chill cake until frosting is firm, 30–40 minutes.

Just before serving, arrange reserved sugared cranberries on top of jam. If using, remove wide pieces of zest from 1 large orange with a vegetable peeler, leaving white pith behind. Cut zest into thin strips and arrange around piped edges of cake. Do Ahead: Cake (without sugared cranberries and orange zest) can be assembled 8 hours ahead. Cover loosely and chill. Let sit at room temperature at least 1 hour before serving.