Toast the sliced almonds in a dry skillet over medium heat, stirring continuously, until lightly golden. Transfer them immediately to a plate to cool.

Whisk 5 egg yolks and the sweetened condensed milk together in a saucepan while it is off the heat.

Place the saucepan over low heat, add the milk, and cook while stirring constantly until the custard thickens to a spreadable consistency.

Remove the custard from the heat and whisk in the vanilla and butter. Press plastic wrap directly against the surface and refrigerate until completely chilled.

Preheat the oven to 350°F and line the bottom of an 8-inch round cake pan with parchment paper.

Beat 4 egg yolks with 1/3 cup sugar and the oil for 1–2 minutes, until lighter in color.

Mix in the almond milk and vanilla or almond extract.

Sift the all-purpose flour, almond flour, salt, and baking powder into the yolk mixture. Whisk until smooth.

Beat the egg whites and lemon juice in a clean, grease-free bowl until frothy.

Gradually add the remaining 1/3 cup sugar and continue beating until stiff, glossy peaks form.

Fold the meringue into the yolk batter in three additions. Fold the final two additions gently to preserve the air.

Pour the batter into the prepared pan. Run a skewer gently through the batter and tap the pan lightly to remove large air pockets.

Bake for 25–30 minutes, until a toothpick inserted in the center comes out clean.

Cool the cake completely before removing it from the pan and slicing it horizontally into three layers.

Spread the chilled custard between the cake layers, then cover the top and sides with the remaining custard.

Press the toasted almonds over the top and sides. Chill until firm before slicing.