In an electric mixer, beat softened butter on low for 1 minute. Then add sugar, and beat on medium until light and fluffy, about 4-6 minutes. Scrape down sides as needed.
Reduce mixer speed to medium-low. Add eggs, one at a time, letting each egg completely incorporate into sugar mixture before adding the next egg. Scrape down sides of bowl as needed.
Add vanilla, and let incorporate.
Add milk, and let incorporate.
In a small bowl, combine flour, baking powder, and salt.
Turn off mixer. Add half of the flour mixture. Turn mixer on low, then gradually increase speed to medium-low. Mix until first half of flour mixture is almost completely incorporated, scraping down as needed. Then add the rest of the flour mixture. Mix until the flour mixture is just mixed into the batter. Batter will be thick.
Heavily grease the inside of both halves of the lamb cake mold with Crisco.
Pour the cake batter into the front half of the lamb cake mold. Using a spatula, spread the batter out to fill every corner. Fill the mold level, do not over fill.