To achieve the Vanilla Bean Latte flavour in the buttercream, I added instant espresso powder (has to be the instant variety), vanilla bean paste (interchangeable with vanilla beans), and a few pinches of cinnamon (which is how I love my lattes). The cinnamon is potent, so only a pinch is necessary--you don't want to overpower the gorgeous vanilla bean and espresso flavours. I've included my ratios in the recipe, but if you try this version, play around, because it really is to taste. 
My recipe also uses a vanilla bean cake, but you could easily try a light espresso cake with vanilla bean buttercream, or you could leave the vanilla bean out of the buttercream and use an espresso buttercream with a vanilla bean cake. I have a feeling you can't go wrong, as long as the flavours aren't overpowering. 
Add a sprinkling of cinnamon before serving, for colour, a few coffee beans for garnish, and voila!
The cake itself is a butter vanilla cake, so the texture is moist but has some density, but is still fluffy with only the egg whites and a generous amount of baking powder. The recipe method is traditional: creaming of the butter & sugar, gradual adding of the egg whites, sifting & whisking of the dry ingredients, and alternating the wet & dry ingredients gently into the batter. I would say this is my go-to vanilla cake recipe, both for cake and cupcakes, because it's simple, delicious, and, yep, quick!
I recently tweaked my Swiss Meringue Buttercream recipe for a lighter, less-buttery, version, and I haven't looked back (although, there are many ratios for SMB, and they all taste fabulous!). This, though, was the perfect, airy, not-too-sweet base for this Vanilla Bean Latte version, with a fluffiness reminiscent of the frothy milk that is happily perched on top of a latte. Delightful.
Vanilla Bean Latte Layer Cake
For the Cake:
- 1-1/2 cups 3 sticks(341 g) unsalted butter, at room temperature
- 2-2/3 cups 540 g granulated sugar
- 9 275 g egg whites, at room temperature
- 4-1/2 cups 570 g all-purpose flour
- 2 tablespoons 22 g baking powder
- 1 teaspoon 6 g salt
- 2 cups 480 ml buttermilk, at room temperature
- 1 tablespoon 15 ml vanilla bean paste or 1 vanilla bean, split & scraped
- 1 teaspoon 5 ml pure vanilla extract
For the Buttercream:
- 6 large egg whites (180 g)
- 1 cup 200 g granulated sugar
- 1-1/2 cups 3 sticks(340 g) unsalted butter, softened but cool, cut into cubes
- 1 teaspoon 5 ml pure vanilla extract
- 1 vanilla bean (split & scraped or 1 tablespoon (15 ml) vanilla bean paste)
- 1 tablespoon 15 g instant espresso powder (or to taste) dissolved into 1 teaspoon (5 ml) boiling water
- 1/4 teaspoon 1.5 g cinnamon (or to taste)
- Pinch of salt
For the Cake:
- Preheat oven to 350° F. Butter three 8" x 2" round cake pans, line with parchment rounds, butter paper and dust with flour, tapping out the excess.
- In a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed until lighter in color and slightly increased in volume, about 5 minutes. Lower the speed to medium and add the egg whites gradually, mixing until fully incorporated.
- Sift the flour, baking powder, and salt into a medium bowl. Mix vanilla extract and vanilla paste (or contents of vanilla bean) into buttermilk. Alternate dry ingredients and buttermilk into creamed mixture, beginning and ending with dry ingredients. Mix until just incorporated or finish by hand gently.
- Divide the batter evenly between the prepared pans. If possible, weigh the batter in each cake pan on a digital kitchen scale to ensure even layers. Smooth with small offset palette knife, and bake for about 30 minutes, rotating once after 20 minutes. Cake is done when toothpick or skewer comes clean. Try not to over-bake.
- Let pans cool on wire rack for 10 minutes, then invert cakes onto racks, gently, peeling away parchment rounds. Let cool completely.
For the Buttercream:
- Wipe the bowl of an electric mixer with paper towel and lemon juice, to remove any trace of grease. Add egg whites and sugar, and simmer over a pot of water (not boiling), whisking constantly but gently, until temperature reaches 160°F, or if you don't have a candy thermometer, until the sugar has completely dissolved and the egg whites are hot.
- With whisk attachment of mixer, begin to whip until the meringue is thick, glossy, and the bottom of the bowl feels neutral to the touch (this can take up to 10 minutes or so). *Don't begin adding butter until the bottom of the bowl feels neutral, and not warm.
- Switch over to paddle attachment and, with mixer on low speed, add butter cubes, one at a time, until incorporated, and mix until it has reached a silky smooth texture (if curdles, keep mixing and it will come back to smooth). *If mixture is too runny, refrigerate for about 15 minutes and continue mixing with paddle attachment until it comes together. Add espresso mixture, vanilla, cinnamon and salt, continuing to beat on low speed until well combined.
Assembly of the Vanilla Bean Latte Layer Cake:
- Place cooled cake layer on cake pedestal, or cake board, face-up. Spread 1 cup of buttercream on top using a small offset palette knife, leaving narrow border along outside edge.
- Gently place 2nd cake layer on top, and be sure to center it with bottom layer. Apply another 1 cup of buttercream and spread as you did the first layer.
- Gently place final cake layer on top, face-down (so the clean bottom side is facing up). Apply a final layer of buttercream.
- Fill a pastry bag fitted with decorative tip (I used Ateco #887), and pipe desired designs on cake to trim and decorate. Sprinkle sliced cake servings with cinnamon, and garnish with espresso beans, Chocolate Crunchy sprinkles or a few Gold Dragees for some extra sparkle (optional).
*This cake is best served at room temperature, and keeps nicely in a cake-keeper for up to 2 days. Swiss Meringue Buttercream cakes are ideally refrigerated after day 2, but should always be served at room temperature, so that it comes back to its light and cloud-like texture; otherwise, it will taste and feel like pure butter!
You may find these previous posts helpful when creating this cake:
1. 50 Tips for Baking Better Cakes 2. Swiss Meringue Buttercream Demystified Good luck & enjoy!
