Preheat your oven to 350°F.
In a large mixing bowl, whisk together the wet ingredients – oil, milk, sugar, eggs, and vanilla extract.
Add the dry ingredients – flour, baking powder, cardamom, and salt. Whisk until just combined.
Pour the cake batter into a prepared pan either circle (8inch) or square (8x8 inch).
Bake at 350°F for 35-40 minutes until cooked through. Cool for 10 minutes in the pan, then transfer to a wire rack to cool completely.
To make the buttercream, use a stand mixer or hand mixer and whip room temperature butter on medium speed until fluffy. Beat in (on a low speed) the powdered sugar and orange zest until combined, mix in the milk, vanilla, and salt. Add more milk as needed to get the desired consistency.