Preheat oven to 350°F (177℃). Prepare a 6-inch half sphere pan with baker's floured cooking spray (or grease and flour pan well). Place flower nail in the base of cake pan.

Combine melted butter, buttermilk, eggs, and vanilla in a large bowl and mix until combined. Add in cake mix and stir until moistened (about 30 seconds), then beat on medium speed for about 2 minutes.

Bake for 35-45 minutes, (or until a toothpick inserted in the center comes out clean). Allow to cool for 10 minutes before removing cake from pan. Repeat with remaining cake batter.

Chill before stacking/decorating. (Place in the fridge to accelerate the cooling process if desired.) While you’re waiting…make your frosting!

Beat together cream cheese and butter; beat in powdered sugar and vanilla until well combined. Add milk if needed until frosting reaches an easily spreadable consistency.

(If desired, use a cake leveler or large serrated knife to slice cake into 2 layers to fill with frosting).

Place a smear of frosting on a plate or cake circle (to keep the cake from sliding while you decorate it) and center the top of one half-shere in the center of the circle. Spread with frosting and repeat with the base of that half-sphere. Insert a straw or dowel in the center for stability (optional but recommended). Repeat in reverse with the other half-sphere (so it looks like a ball when you’re done. ;) )

Add a crumb coat (thin layer of frosting) to the outside, and chill for 20-30 minutes in the fridge or 10-15 minutes in the freezer to set.

Transfer white frosting to a piping bag fitted with a small slotted tip.

All y’all more artistic than me could probably eyeball this part - but I tried free-hand piping this and it was messy, lol. So I grabbed a 2-foot piece of string and used it to create the ‘line’ I wanted - then pressed it into the frosting to make a guideline to follow as I piped (removing the string as I was piping). Whatever method you use, pipe a white line of frosting to the outside of the cake to resemble a tennis ball. Mine was about 3 inches apart at the top expanding to roughly 6 inches at the widest part near the cake base.

(This will be the most time-consuming step-) transfer the yellow-green frosting to a piping bag and pipe small stars covering the rest of the cake. My hand got tired during this step; rotate positions and take breaks if you need to. :) You can probably see in the video - I even laid sideways on the table to pipe near the base of the cake. Go with what works. ;)

Once the cake is covered, set it in the fridge for 20-30 minutes to semi-set the frosting. Then I took a paper towel and gently pressed into the ‘pointy’ parts of the frosting to mute the points a bit - this was the closest I could get to resembling the textured look of a tennis ball.

Transfer green frosting to a piping bag fitted with a grass tip, and pipe a rim of grass around the cake base. High-five yourself on your awesome cake - and enjoy!