Prepare the cake according to the box instructions for two 9in round pans.
Using an electric mixer in a large bowl or a stand-up mixer with the flat beating attachment, beat the softened butter at medium to high speed for about 30seconds.
Scrape the sides and add two cups of sugar. Mix at low speed for about 30 seconds.
Scrape the sides of the bowl. Add one more cup of sugar, 2 tablespoons of milk, and vanilla. Mix at slow speed so the sugar won't blow out of the bowl, then increase speed to medium for about 30 seconds.
Scrape the sides of the bowl, then add one cup of sugar and one tablespoon of milk. Start mixing at slow speed then increase to medium for about 30 seconds.
Scrape the sides of the bowl, then add one cup of sugar and one tablespoon of milk. Start beating at low speed, then increase to medium-high speed until all ingredients are well combined. The frosting should be creamy and easy to spread. You can add more milk, one tablespoon at a time if needed.
When the cake rounds are completely cool make sure they are evenly flat. If they are not, correct as needed. Then place one on the serving plate and spread a generous amount of the frosting on top. Then spread half a cup of the jam. Top with a quarter cup of each of the fruit.
Place the second cake round on top and repeat in the same order: frosting, jam, fruit.
Serve immediately or keep on the fridge for 2 days.