Here is a quick an effective way to make cake doilies. You will need a couple of items but once you have that, it is fairly easy to make. You can find the products in your craft store or online.
First you need to have a filigree piece to your likings. Then you need to make a mold from a two compound mix or at least something that will be flexible and can withstand the oven temperature. ( I will not address mold making here)
With a spatula mix together white pigment powder (chalk) and liquid Fimo. A bit more liquid Fimo than powder.
Mix it with a spatula or butter knife until they are completely blended.
Put a dollop of the mix on your mold and smear it out so you can almost see thru it.
It should look something like this. Put it in the oven and bake according to Liquid Fimo instructions.
Take it out of the oven, and while still hot run it under cold water. Or if you are patient wait until it is completely cold and peel it off.
You might need to trim off excess clay with a fine scissor. Here is one pink doily as well. Just use some pink and white chalk with the liquid Fimo to get that effect.
Here you have the cake doily under the cake, where it should be. Good luck and I hope you liked this mini tutorial.