Preheat oven to 350°F (175°C). Grease two 8-inch round cake pans (and optionally line the bottoms with parchment rounds).

In a large bowl whisk together 4 cups all-purpose flour, 1 tablespoon baking powder, and 2 teaspoons kosher salt until evenly combined.

In the bowl of a stand mixer fitted with the paddle (or in a large bowl with a hand mixer) combine 2 cups buttermilk, 1/4 cup plain Greek yogurt, 1 cup canola oil, 4 eggs, 2 cups granulated sugar, and 1 tablespoon vanilla extract. Beat on medium speed until smooth and combined.

With the mixer on low, add the dry ingredients to the wet ingredients in two or three additions, mixing only until no dry streaks remain and the batter is pourable but not very thin.

Divide the batter into two equal portions in separate bowls. To one portion, add 1/2 cup unsweetened cocoa powder and 1/4 cup black coffee; beat gently until fully combined and smooth. Leave the other portion plain (vanilla).

Assemble the zebra pattern: Working over both prepared pans, spoon about 1/4 cup of the plain batter into the center of one pan, then spoon about 1/4 cup of the chocolate batter directly on top of the vanilla in the same spot. Repeat (vanilla then chocolate) alternating spoonfuls into the center until both pans are filled. You can alternate between pans as you go so they fill evenly. Tap the pans gently on the counter occasionally to help the batter spread; don’t overwork it.

Bake the pans on the middle rack for 35–40 minutes, or until a toothpick inserted in the center comes out clean. Remove from oven, let cool in the pans for 5 minutes, then invert onto a wire rack and cool completely.

Make the chocolate mousse (prepare while cakes cool). Chill the mixing bowl and whisk attachment if possible. Pour 3 cups heavy whipping cream into the bowl and whip to soft-to-medium peaks. Add the remaining 1/2 cup unsweetened cocoa powder (for the mousse), 1/3–1/2 cup honey or powdered sugar (choose one), 2 teaspoons vanilla extract, and a pinch of sea salt. Continue whipping until the mixture is smooth, holds shape, and is spreadable but not grainy. Cover and refrigerate until ready to assemble.

When cakes are completely cool, use a serrated knife to slice each cake layer in half horizontally so you have four even layers total.

Assemble the cake: Place one cake layer on your cake stand or serving plate. Spread an even layer of chocolate mousse over the layer. Repeat with the next two cake layers and mousse, finishing with the top cake layer.

Whip the remaining 1 cup heavy whipping cream in a clean, chilled bowl to stiff peaks. Spread this whipped cream around the outside and over the top of the assembled cake to cover and smooth as desired.

Refrigerate the finished cake at least 30 minutes to allow the mousse and whipped cream to set. Keep the cake stored in the refrigerator and serve within 1 day.