Do I have to use a boxed cake mix?
No, but it is the classic move. A homemade vanilla sheet cake works too, as long as it is sturdy enough to hold the gelatin. Think a standard butter or oil-based vanilla cake, not a super airy sponge. If you go homemade, bake it in a 9x13-inch pan and poke while warm.
When do you poke the holes?
Poke the cake while it is still warm, about 10 minutes after it comes out of the oven. Warm cake absorbs the gelatin better and gives you those pretty strawberry streaks.
How big should the holes be?
Use the handle of a wooden spoon or a thick straw. You want holes about the size of a pencil. Too tiny and the gelatin cannot really get in there. Too huge and the cake can turn a little mushy in spots.
Can I use sugar-free gelatin?
Yes. It still works, but the set and flavor can vary a bit by brand. If your gelatin seems to set softer, just give the cake a full overnight chill.
What topping is best: whipped topping or homemade whipped cream?
Both work. Store-bought whipped topping is the most stable for parties. Homemade whipped cream tastes extra fresh, but it can weep after a day. Powdered sugar helps a little; for extra insurance, use a stabilizer like a pinch of instant pudding mix or a small amount of bloomed, melted gelatin. Either way, homemade is best within 24 hours.
Why is my cake soggy?
Usually it is one of these: holes too large, gelatin poured too fast in one area, or cake not chilled long enough to set. Next time, pour slowly and evenly and give it a full chill.