Preparation Steps

• Heat the oven to 340°F (170°C). Grease two 8-inch round cake pans, line the bottoms with parchment, and dust the sides with cocoa. Set aside.
• In a large bowl, whisk together the flour, cocoa powder, espresso powder, baking soda, and salt until evenly combined.
• In a stand mixer (or with a hand mixer), beat the sugar and eggs on medium-high speed for 2 minutes until paler and slightly thickened.
• With the mixer running on low, slowly stream in the oil, then the melted butter. Mix in the sour cream, vanilla, and orange zest just until smooth.
• Combine the buttermilk and 1/3 cup spiced rum in a measuring cup. On low speed, add the dry ingredients to the egg mixture in three additions, alternating with the buttermilk-rum mixture (begin and end with dry). Mix just until no dry streaks remain; do not overbeat. Scrape the bowl and fold once by hand.
• Let the batter rest for 5 minutes to hydrate the cocoa, then divide evenly between the prepared pans. Smooth the tops and tap each pan firmly on the counter to release large air bubbles.
• Bake for 24–29 minutes, rotating the pans once halfway. The cakes are done when the centers spring back lightly and a toothpick comes out with a few moist crumbs. Cool in pans on a rack for 10 minutes.
• While the cakes bake, make the syrup: In a small saucepan, melt the butter over medium heat. Stir in the water and sugar, bring to a gentle boil, and cook for 4 minutes, stirring often. Remove from heat and carefully stir in the rum (it will steam). Keep warm.
• Turn the cakes out onto wire racks and peel away the parchment. While still warm, brush each layer generously with about half of the warm rum syrup, letting it soak in before adding more.
• Place one layer on a serving plate, brush with a little extra syrup, then set the second layer on top. Brush the remaining syrup over the top and sides for a glossy finish. Let the cake stand 30–45 minutes to set before slicing.