Preheat oven to 350°F (177°C). Lightly grease four 8 x 2-inch round cake pans. Line the bottoms with parchment paper rounds. Flour the sides and tap out any excess flour.
In the bowl of a stand mixer fitted with the paddle attachment, combine flour, the Redpath® Golden Yellow Sugar, the Redpath® Granulated Sugar, baking powder, baking soda, and salt. Mix on low speed until thoroughly mixed, and no lumps remain.
Add the cubed butter and mix on low speed until all the dry ingredients are coated, and the mixture looks like wet sand.
Add the eggnog and canola oil. Mix on low speed until just combined. Scrape down the sides of the bowl and increase the speed to medium speed; beat for 30 seconds.
In a large measuring cup, whisk together the eggs and yolk. With the whisk, carefully stir in the sour cream and vanilla extract until well combined.
Add ⅓ of the egg-sour cream mixture into the bowl of the stand mixer. Beat on low speed until just combined, increase speed to medium, and beat for 30 seconds to incorporate. Repeat process with the remaining egg-sour cream mixture.
Divide the batter evenly between 2 large bowls; use a scale for greater accuracy.
In a small bowl, whisk together cocoa powder and instant espresso. Add and whisk in the hot water. Set aside to cool slightly.
In one of the bowls, sprinkle the nutmeg and cinnamon over the surface of the batter. Gently fold in with a large spatula until well combined. Divide the batter evenly into 2 of the prepared pans (again, use a scale for more accuracy). Spread and smooth out the tops using a small offset spatula.
Add a dollop of the untouched batter into the cocoa powder mixture to help loosen it up. Stir well. Add the cocoa mixture into the larger bowl and fold with a large rubber spatula until thoroughly mixed. Divide the batter evenly into 2 of the prepared pans. Spread and smooth out the tops using a small offset spatula.
If oven is not large enough, bake 2 pans, one of each flavour, at a time. Cover and set the other 2 pans in a cool area while the other cakes bake.
Place cakes into the preheated oven and bake for 30 to 35 minutes or until a skewer inserted into the centre come out clean. Note that the eggnog cakes may bake faster than the cocoa cakes. Remove baked cake(s) from the oven as they are ready.
Place cakes onto wire cooling racks and allow to cool; 10 minutes.
Run a small offset spatula around the edge of each cake. Carefully flip cakes out and place them onto the wire cooling racks. Allow them to cool completely before attempting to cut (see Chef’s Tips); 1 to 2 hours.
While the cakes are cooling, make the buttercream.