Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, almond flour, baking powder,and salt until well combined. Set aside.
Combine milk and Amaretto. Set aside
Using a stand mixer fitted with a paddle attachment, cream butter and sugar on med-high until pale and fluffy (approx 3mins). Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and milk mixture, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition.
Bake for approx. 35mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack. Allow cakes to cool completely.
Place sugar and water into a small pot. Bring to a boil and simmer 2 mins. Remove from heat, stir in Amaretto. Cool completely
Vanilla Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a double boiler on the stove and whisk constantly until the mixture is hot (160F) and no longer grainy to the touch (approx. 3mins).
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.** Add vanilla and mix until incorporated.
Trim tops of each cake layer just slightly (to help the syrup absorb).
Place one layer of cake on a cake stand or serving plate. Brush generously with Amaretto Syrup. Top with approximately 2/3 cup of buttercream and spread evenly. Repeat with remaining layers.
Frost and smooth the outside with a thin crumb coat. Chill for 20mins. Frost the top and sides of the cake and pipe dollops on top of desired using an Ateco 867 or Wilton 6B tip.
Press toasted almonds into the bottom and sprinkle on top of the cake.
* Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen. ** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth.Note: - If you don't have almond flour and can't be bothered buying it (I don't blame you), you can just leave it out and increase the flour to 2 1/4 cups. - If you prefer a non-alcoholic version, you can use almond extract instead. For the cake, use 1/4 - 1/2 tsp almond extract (at most) and increase the milk to 1 cup. For the syrup, use 1 tsp of almond extract instead of Amaretto. Almond extract is strong and it's easy to overdo it. Less is more here.