I make a really bomb caramel cake, but the only problem I have is that my frosting gets a bit granulated. Is there anything I can do to keep my frosting smooth and soft? Below is the recipe for my frosting, any tips are appreciated. Thanks.

Icing
1 cup white sugar
1 cup brown sugar
1 stick butter
1 14 oz. can Eagle Brand milk
1 tsp. vanilla
Combine all ingredients in saucepan and cook
2 minutes, stirring constantly, until thick and
Bubbly. Remove from heat and let cool until fairly thick
And just warm. Pour over cakes and assemble layers.
Keep piling icing back onto cake with knife until
Cooled.*

It gets grainy when you scrape undissolved sugar down off the sides of the pot back into the cooking mixture. That gives the mixture unevenly dissolved granules. Stop scraping too late during the cooking process.

Instead, heat the mixture gently and thoroughly to ensure the sugar has completely dissolved. Meanwhile, scrape down sugar crystals on the side of the pan. When the sides of the pot are "clean" and the sugar has dissolved, then and only then boil the mixture for two minutes.

Source: my 87-year-old mother

Cool, mom! I never knew that.

The sugar crystals must be dissolved evenly. It needs patience in stirring and low heat melting.