How can I make a decorative cake frosting that tastes delicious?

make a flavored buttercream frosting! you can even put it in the fridge to help it firm up a bit.

For the almond meringue buttercream:
4 egg whites
¾ cup + 3 tablespoons sugar
2 ½ sticks (10 ounces) unsalted butter, cut into small chunks and at room temperature
½ teaspoon almond extract

Almond meringue buttercream:
Add the egg whites and sugar to the bowl of a standing mixer. Put 1–2” of water in a small saucepan and bring it to a boil. Reduce the heat so that the water simmers. Put the mixer bowl on top of the saucepan and whisk the egg whites and sugar until all of the sugar has dissolved, the mixture becomes opaque, and the temperature reaches about 110 F. (If you do not have a thermometer, don’t worry. Just make sure that all the sugar is dissolved and that the mixture is very warm – this will take about 3–4 minutes.)

Put the bowl on the mixer and whip the whites (using the whisk attachment) for 8 minutes on high speed (mixer speed 10). They whites will be very thick and glossy and the bowl should be completely cool the touch. If the bowl is not cool, continue beating until it is.

With the mixer running on high speed, add the butter to the bowl one piece at a time, waiting until each piece is incorporated before adding the next. After all the butter has been added, continue beating until the mixture becomes very thick and smooth and looks like frosting.

Add the almond extract and mix on medium speed for 10 seconds to fully incorporate. Switch to the paddle attachment and beat on low speed (2 or 4) to remove air bubbles from the frosting.

it would be nice to have a lemon frosting because it is a very nice tangy and sweet flavour added together.