Preheat the oven to 350℉. Spray 2 9" round pans or 3 8" round pans with cooking oil spray. Set aside.

In a large mixing bowl, cream the oil, eggs, whole milk, lime zest, and lime juice for 2 minutes.

In another large bowl, stir together the flour, sugar, baking powder, baking soda, and salt. Stir the flour mixture into the egg mixture, folding gently.

Divide the batter between 2 or 3 pans. Bake for 20-26 minutes or until a toothpick comes out clean. If using the two 9" pans, bake for 30-36 minutes. Cool the cakes on a baking rack.

In a large bowl, cream together the butter and cream cheese until light and fluffy between 8-9 minutes. Add 4 cups of the powdered sugar, lime juice, lime zest, and beat until blended. Only add the extra sugar if it's too wet. Chill while cake cools.

When cool, remove the cakes from their pans. Spread the frosting on one cooled cake layer, place the next layer on top, and cover with frosting. If using 3 cakes, repeat with the third layer. Garnish with lime slices.