For the cupcakes:Preheat the oven to 350 degrees F and line about 14 muffin cups with paper liners.
Melt together the butter and chocolate in the microwave, heating in 20-30 second increments and stirring each time until smooth. Set aside to cool slightly.
In the bowl of a stand mixer (or in a large bowl with an electric mixer), combine eggs, sugar, vanilla and yogurt until smooth.
Add melted chocolate mixture and beat until combined.
Add cocoa, flour, baking soda, baking powder and salt and beat just until combined. Batter will be thick and almost mousse-like in texture.
Spoon into prepared muffin pans, each cup about ⅔ full, and bake for 15 minutes or until a toothpick inserted in the center comes out clean. Cool to room temperature.
Frosting:In a stand mixer (or in a large bowl with an electric mixer), beat butter until smooth. Add powdered sugar, vanilla and milk and beat on low until combined. Beat on high 1-2 minutes until fluffy and smooth.
To make the cupcake cake:Divide frosting into 4-5 small bowls and color with food coloring as desired. I had brown for the base, red, burgundy, green, and warm yellow.
I find the frosting gets warm after mixing the food coloring in and I like to cover and refrigerate at least 1-2 hours before piping.
Place frosting in separate piping bags -- the brown fitted with a small round tip, the colors fitted with leaf tips (or use couplers if you don't have enough leaf tips to go around -- then you can easily switch the tips).
Arrange cupcakes in a circle (can be as small or large as you want). Pipe the brown frosting in circles around the top of the cupcakes to form the base of your wreath. Try to cover as much of the top as possible -- this will keep your leaves from sinking in the cracks.
Pipe different colored leaves all around the cupcakes until you are happy with the colors and fullness.
*To pipe a leaf with your leaf tip: Hold the piping bag so the tip has one point to the sky and one point to the bottom (the cupcake). Squeeze the bag and hold the tip in place to build the base of your leaf. Slowly move the tip out and release pressure on the bag, dragging the tip out to make the point. They won't all be perfect -- and that's okay! You can always do another one on top of the ones you dislike.