Preheat the oven to 350F/177C. Line three, 8-inch (20-cm) cake pans with parchment paper and spray the sides with a baking spray, if desired.
In a large mixing bowl, combine the liquid ingredients: buttermilk, cooking oil, vanilla, eggs and pure maple syrup. Mix the ingredients together on medium speed for 2 to 3 minutes, until the eggs are well beaten.
In a separate bowl, combine the dry ingredients: flour, baking powder, baking soda and salt. Sift the dry ingredients into the liquids and mix on low speed for 1 minute, just until the flour is incorporated. Gently fold in the diced pecans last.
Divide the cake batter evenly between the three prepared pans. Bake the cake layers in the preheated oven for 25 to 28 minutes, or until a toothpick inserted into the center comes out clean. The tops should be a rich, golden color. Allow the cake layers to cool in the pans for 5 minutes, then let them cool completely on a wire rack.
For Maple French Buttercream:
Prepare the maple buttercream next. Place the egg yolks into a mixer bowl and whisk on high speed for 2 to 3 minutes, until the yolks are thickened and pale. Meanwhile, pour the maple syrup into a small sauce pot and attach a candy thermometer to the side.
Cook the maple syrup over medium heat until the temperature reaches 240F/115C. This usually takes about 5 to 7 minutes. Watch the maple syrup as it heats; it can foam up and bubble over the top of the pot. If the maple syrup foams and bubbles, remove it from heat until it settles, then continue cooking on a lower heat.
Once the syrup comes up to temperature, immediately turn on the mixer to a medium speed and slowly pour the maple syrup into the egg yolks in a slow and steady stream. Once all the maple syrup has been added, increase the mixer speed to high and mix for 7 to 9 minutes, until the egg yolks are fluffy, thickened and pale in color. The mixture should also be cooled down until it’s barely warm.
Slowly start to add the butter, a few tablespoons at a time. Continue adding the butter even if the frosting looks separated; the frosting will come together. Once all the butter is added, add in the vanilla. Turn the mixer up to high speed and whisk for another 3 to 4 minutes, until the frosting is creamy and smooth.
Assembling the Maple Pecan Cake:
To assemble the cake, first make sure the cake layers are completely cooled. Use a long, serrated knife to level off the top of each layer. Using a pastry brush, lightly soak each layer with maple syrup, then top with a layer of the prepared buttercream. Use an off-set spatula to spread the frosting evenly. Watch my video recipe to see how it’s done.
Frost the top and sides of the cake with a crumb coat of frosting, then set the cake into the refrigerator to chill for 15 to 20 minutes. Apply the final layer of frosting and smooth the sides and top of the cake. Using your hands, very gently press the remaining diced pecans into the sides of the cake and sprinkle some on top. If desired, transfer any remaining frosting and add dollops of cream on top of the cake. I used a French star tip #4 for my cake.
The cake can be enjoyed right away or refrigerator for later. If refrigerated, remove the cake about an hour before serving to allow the buttercream and cake to soften.