01 - Preheat oven to 350°F (175°C). Grease a 9-inch round cake pan and line the base with parchment paper.
02 - Whisk together almond flour, all-purpose flour, baking powder, and salt in a medium bowl.
03 - In a large bowl, beat eggs and granulated sugar until pale and slightly thickened, about 2 minutes.
04 - Mix olive oil or melted butter, vanilla extract, orange zest, and orange juice into the egg mixture until combined.
05 - Fold the dry ingredients into the wet mixture gradually until just combined; avoid overmixing.
06 - Pour batter into prepared pan and sprinkle sliced almonds evenly on top.
07 - Bake for 35 to 40 minutes until a toothpick inserted in the center is clean and the top is golden brown.
08 - Allow cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
09 - Dust with powdered sugar and garnish with orange slices before serving, if desired.