Cake – Mirror Glazes and Freezing: What You Need to Know

According to Shirley Corriher, as reported in Fine Cooking, the sugar should weigh slightly more than the flour:

The sugar should weigh the same as, or slightly more than, the flour. Remember that this is weight, not volume. A cup of sugar weighs about 7 ounces, and a cup of all-purpose flour weighs about 4-1/2 ounces. So, if we're building a recipe with 1 cup sugar, we'll need about 1-1/2 cups flour (about 6-3/4 ounces).

Sugar plays a very important role in creating the structure and bite of cakes, and also helps to retain moisture and inhibit spoiling, so you cannot simply reduce the quantity without limit to control the sweetness.

That being said, most recipes have a certain amount of tolerance. You can probably reduce the sugar by about 20 to 25% without completely altering the nature of the recipe, although the crumb may suffer a little.

Vanilla and rose are delicate flavors. If you are making a yellow cake with butter, and egg yolks, they may be competing and masking the flavor.

Using a white cake base may allow these flavors to show through more clearly.

Put them in the freezer on your parchment covered baking sheet for an hour. Get your Tupperware and cover the bottom with a folded paper towel. Then remove the flowers and put them in the Tupperware. Cover the flowers with another paper towel and seal the Tupperware tight.

The paper towels will help keep them container somewhat desiccated so the flowers don't get damaged by condensing ice crystals and freezer burn. I wouldn't leave them in there for too long though, because they will get burned after some time no matter what you do because of the air space in the Tupperware. Use them within a day or two if you can.