Preheat the oven to 176°C and lightly grease and line a 8"x 8" square cake pan with baking parchment.
In a bowl, whisk together the flour, salt, caraway seeds, baking soda and baking powder.
In a larger bow, whisk the oil, buttermilk, vinegar and jaggery powder till you get a smooth, liquid without any lumps of jaggery.
Now fold the dry mixture into the wet mixture till just combined. Do not overmix.
Pour the batter into the prepared pan. Tap it a few times to remove any air bubbles, and bake in the oven for 35-40 mins. Test the cake for doneness by inserting a skewer or toothpick in the centre; the skewer should come out dry.
Cool the cake in the pan for 10 minutes before un-molding and cooling on a wire rack. Store in an airtight box.