Preheat oven to 350 °F (175 °C). Line a 10 × 15 inch jelly-roll pan with parchment paper.

In a big bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt.

In another bowl, beat eggs and sugar until light and foamy (about 2 minutes). Then pour in the oil and keep whisking until silky.

Add the dry mixture slowly to the wet, stirring just until the flour disappears—don’t overmix or your sponge gets tough. Then fold in the shredded carrots and nuts or raisins if using.

Spread the batter evenly into your pan. Bake for 12–15 minutes. When a toothpick comes out clean, it’s done.

Right out of the oven, flip the cake onto a clean towel dusted with powdered sugar. Roll it up (cake + towel) while still warm—this trains the sponge to hold its shape later. Let it cool completely.

Beat cream cheese and butter until creamy, then slowly add powdered sugar and vanilla. The result should be smooth, glossy, and dangerously lickable.

Unroll the cooled cake, spread the frosting evenly, then gently roll it again (without the towel). Wrap it in plastic and refrigerate for at least an hour.

Dust with powdered sugar, decorate with nuts, and serve those lovely slices.