Preheat the oven to 325°F and lightly grease a 9x13-inch baking dish. In a large mixing bowl, blend the cream cheese until creamy, then incorporate the vegetable oil and granulated sugar. Beat in the eggs one at a time, ensuring each is fully mixed before adding the next, and stir in the vanilla extract. In a separate bowl, sift together the flour, baking powder, and salt. Gradually fold the dry mixture into the wet ingredients until just combined. Add the buttermilk and stir gently until the batter is smooth and uniform. Pour the batter into the prepared dish and bake for 35 to 40 minutes, or until a toothpick inserted in the center emerges clean. Let the cake cool completely.

To prepare the frosting, beat together the cream cheese and butter in a large bowl until fluffy. Slowly add the powdered sugar, mixing until smooth, then blend in the salt and vanilla. Once the cake has cooled, evenly spread the frosting over the top. Refrigerate until ready to serve.