For the Sponge Cake:
1 cup sifted cake flour
3/4 cup granulated sugar
5 large eggs room temp
For the Syrup:
1/4 cup granulated sugar
3/4 cup hot water
3 Tbsp rum – I used Bacardi golden rum optional, but adds great flavor
For the Custard Buttercream Frosting:
1 egg yolk
1/2 tsp vanilla extract
1/2 Tbsp water
1/2 cup sweetened condensed milk uncooked – straight from the can
1 cup 2 sticks unsalted butter
1/2 Tbsp olive oil
4 Tbsp cocoa
For the Topping:
1/2 cup golden brown cookie crumbs I used crumbs from 4 graham crackers
What you’ll need:
11 ×17 rimmed baking sheet lined with parchment paper
How To Make the Sponge Cake:
- Preheat oven to 410˚F.
- Beat 5 eggs with white sugar on high speed for 5-6 minutes or until thick and fluffy. Next, sift in 1 cup of cake flour in two intervals and fold gently, scraping from the bottom, just until combined with no streaks of flour remaining. Spread batter evenly onto your prepared baking sheet. Bake at 410˚F for approx. 7-8 minutes or until the top is golden.
- Once the cake comes out of the oven, remove it from the baking pan, and while it’s still hot, place a sheet of parchment or wax paper over it and roll the cake loosely (rolling it while it’s still warm helps prevent cracks later). Let the rolled cake cool to room temp, then you can remove the backing and lay it flat again keeping the same side up as before so you are rolling in the same direction after it’s frosted. (Start making syrup and frosting – see how to make frosting below).
How To Make Syrup:
- Dissolve sugar in boiling water. Add rum and let the syrup cool to room temp.
How To Make Vanilla and Chocolate Custard Buttercream:
- In a small sauce pan, off the heat, whisk together 1 egg yolk, 1/2 Tbsp water, 1/2 cup condensed milk, and 1/2 tsp vanilla until smooth.
- Place over the lowest heat and slowly increase the heat to a medium/low or just until it is lightly steaming. Continue whisking constantly until it thickens slightly – don’t let it boil. When it’s ready, it will be the consistency of uncooked sweetened condensed milk. Total time on the stove: 7-8 minutes. Remove mixture from heat and let custard cool to room temp. It will thicken more as it cools.
- Beat softened butter in a mixer with whisk attachment for 5 minutes on high speed, scraping down the bowl as needed.
- Add room temp custard mixture, 1 Tablespoon at a time, into the whipped butter, beating on high speed for a few seconds with each addition. Once all of the custard is incorporated, scrape down the bowl and beat another 2 min on high speed.
- Divide finished cream in half. The first half will remain your white cream and you will spread this over the moistened cake. Keep the second half in the mixing bowl with the whisk attachment and add 4 Tbsp cocoa (1 Tablespoon at a time) and 1/2 Tbsp olive oil. The oil will enhance the chocolatey color. Beat on high speed 2 minutes or until all of cocoa is well incorporated (scrape down the bowl as needed).
Final Cake Assembly Instructions:
- Once cake is room temp, brush the top of your unrolled cake roll (the side that will be the inside once it’s rolled up) evenly with the syrup (see how to make syrup instructions above). Let it sit and soak up the syrup at least 5 min.
- Spread your white cream filling in a thin layer evenly over the top of the cake and start rolling your cake from the same side as before, keeping a tight(-ish) roll without squeezing out the frosting. It really is just a very thin layer of frosting, but it will be just right; you’ll see!
- Next, spread a thin layer of chocolate cream over the top of your cake. You need just enough to cover the cake and keep the crumbs on the sides.
- Sprinkle finished roll with cookie crumbs on the sides; it was easy with a food scraper; pour crumbs along the base of the cake and use a scraper to pull them up on the sides of the cake. Pipe remaining chocolate over the top of the cake. I made swirls across the top with a large Wilton 1M open star tip. Refrigerate cake until ready to serve.
Once the cake is chilled, it is much easier to transfer and slice. It tastes great cold straight out of the fridge or softened up to room temp.