For the cupcakes: Preheat the oven to 350 degrees F. Line two 12-cup muffin tins with paper liners.
In a large bowl, whisk to combine the flour, baking powder and salt; set aside.
In a stand mixer fitted with the paddle attachment, cream the butter and granulated sugar together on medium-high speed until light and fluffy, scraping the sides of the bowl with a rubber spatula periodically, 3 to 5 minutes. Add the eggs one at a time, beating well after each addition, followed by the sour cream and vanilla extract; mix to combine.
Turn the speed down to low and add the flour mixture and milk in 3 additions, starting and ending with the flour. Use a rubber spatula to scrape down the sides of the bowl. Divide the batter evenly among the muffin cups, filling each about two-thirds full. Bake until a toothpick inserted in the center of a cupcake comes out clean, 18 to 20 minutes. Cool completely on wire racks, then decorate.
To decorate: To make a cow, frost the cupcakes with white icing. Place 2 candy eyes in the center of the icing, then place a round gummy peach below the eyes. Use soft black licorice sticks to make ears and 2 jelly beans to make horns at the top of the head.
To make a pig, frost the cupcakes with pink icing. Place 2 candy eyes in the center of the icing, then place a round gummy peach below the eyes. Cut a gummy peach into triangles and use 2 pink pieces for the ears.
To make a sheep, frost the cupcakes with white icing. Place 2 eyes in the center of the icing. Cut a gummy peach into triangles and use 2 orange pieces for the ears. Place 1 jelly bean in the center of the cupcake below the eyes to make a nose. Place mini marshmallows all over the remainder of the icing, pressing gently to adhere.
To make a chicken, frost the cupcakes with white icing. Place 2 candy eyes in the center of the icing. Place a jelly bean below the eyes for the nose and a red jelly bean at the bottom of the cupcake for the "wattle." Place 3 jelly beans in a straight line at the top of the cupcake to make the "comb" on its head.
Yield:3 cups icing
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed until smooth. Reduce the speed to medium-low and add the confectioners' sugar, about a cup at a time; mix until completely combined. Add the milk and vanilla extract, and beat until smooth and spreadable.
Place 2 cups icing in a separate bowl and add 2 to 3 drops pink food coloring if using. Stir to incorporate.