This is a super-simple way to add a little fun to a fruit pie or tart. I recommend only using fairly soft fruits (ie. not apples), and cutting the slices as thinly as possible. It takes a little longer and a little more concentration, but it shortens cooking time, and ensures that the slices will bend more easily.
1) Core or pit fruit and cut it in half.
2) Slice each half thinly (don't worry if you can't get all the way to the ends).
3) Curl the first slice into a cone, with the skin side up.
4) Add the rest of the slices, one at a time, around the cone, overlapping each slightlyand keeping the peel facing up. It's OK that the slices aren't all exactly the same size - that's part of what makes these look more like real roses.
5) Transfer to the dish that you're planning to bake in. I like to use a knife to do this, because the fruit can be really slippery, and it's no fun to have it fall apart after all your hard work!
6) Repeat as neccessary, until you have filled the dish. Depending on the nature of the baked good (and the size of your roses), you may want to use fewer or more roses. Less tightly packed means that the roses will naturally open up more, and fewer means that they will stay closer to the shape that you placed them in. In a tart that mostly fruit, I tend to keep them more tightly packed, and in a pie or cake with more filling, I tend to leave the fruit looser - go with your instincts.
With the TWD cake, I left the roses more loosely packed, and pushed them down a little into the filling to make sure that the thicker cake got in between the rose petals.