Make the Cranberry Jam: Combine sugar, salt, cinnamon (if using), and water in a saucepan. Bring to a boil, stirring until sugar dissolves. Add cranberries and simmer until they pop and the mixture thickens, about 15–20 minutes. Let cool completely before using or refrigerate up to 5 days.
½ cup granulated sugar, ¼ teaspoon salt, ½ teaspoon ground cinnamon, ¼ cup water, 1½ cups 6 ounces fresh cranberries
Preheat and Prepare Pans: Preheat the oven to 350°F. Butter and flour three 8-inch round cake pans, then line the bottoms with parchment paper.
Mix Wet Ingredients: In a bowl, whisk together milk, egg whites, sour cream, and vanilla until smooth.
1 cup whole milk, 1 cup egg whites, ½ cup sour cream or crème fraîche, 1 tablespoon vanilla extract
Combine Dry Ingredients: In a stand mixer, mix flour, sugar, baking powder, and salt on low speed. Add butter pieces a few at a time until the mixture looks like coarse sand.
2¾ cups all-purpose flour, 2 cups granulated sugar, 4 teaspoons baking powder, 1 teaspoon salt, 1½ cups 3 sticks unsalted butter, room temperature
Make the Batter: Slowly pour in about half the wet ingredients while mixing on low. Increase to medium speed for 30 seconds, then add the rest and beat until smooth. The batter may look slightly bumpy—that’s okay.
Bake the Cakes: Divide batter evenly into the pans, smooth the tops, and tap gently on the counter. Bake 28–35 minutes or until a toothpick comes out with a few crumbs. Cool in pans for 30 minutes, then remove to wire racks to cool completely.
Make the White Chocolate Buttercream: Melt white chocolate in a heatproof bowl set over simmering water, stirring constantly. Let cool slightly. Beat butter in a mixer until pale and creamy, about 3 minutes. Add corn syrup and salt, mixing well. Gradually beat in powdered sugar until fluffy. Mix in cooled white chocolate, heavy cream, and vanilla until smooth.
1 cup 2 sticks unsalted butter, room temperature, cut into small pieces, White Chocolate Buttercream, 8 ounces white chocolate, 3 tablespoons light corn syrup, Pinch of salt, 2 cups powdered sugar, 2 tablespoons heavy cream, 1 tablespoon vanilla extract
Make the Sugared Cranberries: In a saucepan, heat ¾ cup water, ¾ cup sugar, and salt until the sugar dissolves and slightly thickens, 5–7 minutes. Remove from heat, stir in vanilla, and pour over cranberries in a bowl. Cover and refrigerate for at least 8 hours or overnight. Drain, then roll cranberries in remaining ½ cup sugar. Spread on a baking sheet to dry.
¾ cup water, 1¼ cups granulated sugar, 1 teaspoon vanilla extract, 1½ cups 6 ounces fresh cranberries, Pinch of salt
Assemble the Cake: Place one cake layer on a plate or stand. Spread about 3 tablespoons of cranberry jam on top. Add the second layer, spread with another 3 tablespoons of jam, then top with the final cake layer. Frost the entire cake with white chocolate buttercream.
Decorate and Serve: Top with sugared cranberries for a simple, elegant finish. Store covered in the fridge for up to 2 days and bring to room temperature before serving.