Preheat your oven to 350°F (175°C). Grease and flour a 9-inch (23cm) round cake pan or line it with parchment paper.
In a large mixing bowl, whisk together the granulated sugar, almond flour, all-purpose flour, baking powder, baking soda, and salt until well combined.
In another bowl, beat the eggs until frothy. Add the vegetable oil or melted butter, orange juice, orange zest, and vanilla extract. Mix until everything is well combined.
Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Be careful not to overmix.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Remove the cake from the oven and let it cool in the pan for about 10 minutes. Then, carefully transfer the cake to a wire rack to cool completely.
Once the cake has cooled, you can dust it with powdered sugar and garnish it with sliced almonds, if desired.