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.
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 and almond extract.
Alternate adding flour mixture and milk, 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.
Coconut Custard (make in advance):
Place 3/4 cup coconut milk and vanilla into a medium saucepan. Cook over high heat, stirring often until it just starts to simmer. Remove from heat.
In a medium bowl, whisk remaining 1/4 cup coconut milk, egg yolk, sugar, and cornstarch.
While whisking vigorously, slowly pour the hot milk into the egg mixture.
Return mixture to saucepan and cook over high heat, whisking constantly, until it thickens and comes to a boil.
Pass through a strainer and into a small bowl. Place plastic wrap directly on top of custard to prevent a skin from forming. Cool to room temperature then place in refrigerator a couple hours to set.
Coconut Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a pot with 1-2" of simmering water and stir constantly with a whisk until the mixture is hot and no longer grainy to the touch or reads 160F on a candy thermometer (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 coconut milk powder, almond extract and mix until smooth and fluffy.
Assembly:
Place one layer of cake on a cake stand or serving plate. Drizzle or brush with simple syrup (optional).
Do a thin coat of buttercream on the layer and pipe a dam around the edge using a large round tip to hold in the custard. Fill center with half of the custard (about 1/2 cup) and spread evenly. Sprinkle with about 2 Tbsp sliced almonds (more if you like). Repeat with next layer.
Top with final layer of cake. 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 using an Ateco or Wilton 1M tip, top each with a Raffaello if desired.
Gently press shredded coconut into the sides of the cake.
Notes
* 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.