To make the cupcakes:
Preheat the oven to 350degreesF with a rack in the center of the oven. Line muffin tins with 16 "Texas" liners or 24 regular cupcake liners.
Sift together the flour, baking powder, baking soda and salt, set aside.
Combine the melted butter with the sugar in a stand mixer fitted with a paddle attachment, beat on medium speed for 1 minute. Add the eggs, egg yolks and vanilla, mix on medium speed for 3 minutes.
Add a third of the flour mixture to the butter mixture and mix to combine on low speed. Add half of the buttermilk and mix to combine. Repeat with another third of the flour and the rest of the buttermilk, ending with the last third of flour, mixing after each addition. Mix the cake batter on medium-low speed for 1 minute.
Scoop the batter into the cupcake liners, not filling more than half way. You may end up having to fill a few more cupcake liners, but don't overfill.
Bake for about 20 minutes, or until a tester comes out clean. Let the cupcakes cool completely before decorating.
To make the Frosting:
Cream together the butter, shortening and sugar until perfectly smooth. Add the cream one tablespoon at a time until it is nice and creamy, but still holds its shape. Cover tightly if you don't use it immediately or it will develop a crisp crust.
You can use it white or tint the frosting with food coloring. I usually divide the frosting into a few bowls and color each a different color. Cover the frosting when not using.
To decorate your cupcakes with roses:
Using a disposable pastry bag, fitted with a large rose tip (Ateco #128) and an extra large rose nail (Ateco #914) you can create these large colorful roses.
Start by lining up the narrow end of the rose tip with the seam of the pastry bag. Place a thin line of the food coloring along the seam of the bag, that leads to the narrow end of the tip. Fill the bag half way with the frosting.
Once your pastry bag is set up with frosting you will create a mound of frosting on the rose nail. This will be the base of your rose. If the mound is too small your rose will tip over as you are piping it. Making it nice and broad along the bottom is key.
Hold the bag at a 45degrees angle, wide end of the tip touching the mound you just created, near its top. The narrow end of the tube should be nearly straight up and pointing toward the center of the nail.
Squeeze out a ribbon of frosting and turn the nail, holding it between your thumb and forefinger, counter clockwise; swing the rose tip up, around the top of the mound and back down to the starting point. This creates the rose bud.
Now make the first row of 3 petals. Hold the tip so the wide end is touching the mound about half way up, starting right where the bud finished off. Tilt the narrow end of the tip slightly away from the center. Squeeze out the frosting, turning the nail counterclockwise and move the tip up (increase the pressure) and then down (decreasing the pressure) in an arch. Form all three petals in this way, starting each one where the last petal finished.
Pipe a second row of 5 petals, under the row you just finished. Tilt the tip out even more with this row so the petals appear to be opening up. Overlap the petals to hide any openings between them.
You can stop at this point or continue on with a third row of 7 petals.
It may take you a few roses to get the hang of it, but then it will go together very fast. Once you are happy with the size and shape of your rose, take a pair of kitchen shears and cut the base of the rose off of the nail. You will want to cut only part way through, so you can lift up the rose on the blades of the shears. Then place the rose on the cooled cupcake. You can pipe leaves at the base of the rose with a leaf tip.