Preheat oven to 350°F (175°C) and grease a 9x13-inch pan or two 9-inch round pans.
Whisk flour, baking powder, baking soda, salt, cinnamon, and nutmeg in a bowl.
In another bowl, beat oil, sugars, eggs, and vanilla until smooth.
Stir dry ingredients into wet mixture until just combined.
Fold in grated carrots, nuts, and raisins gently.
Pour batter into prepared pan and bake 30–40 minutes until a toothpick comes out clean.
Cool completely before frosting.
Beat cream cheese and butter until smooth, add powdered sugar and vanilla, and spread over cooled cake.