In a medium saucepan whisk together sugar, cornstarch, salt, milk, and egg yolks. Cook over medium-low heat, whisking occasionally, until the mixture is bubbling (about 7-8 minutes). Continue cooking while bubbling for 1-2 additional minutes.
Remove from heat and whisk in butter and vanilla extract.
Transfer the pudding into a large bowl. Cool until lukewarm, then cover with plastic wrap. Refrigerate for 2 hours or until chilled.
Place in bunny glasses and top with french palmier cookies to make bunny ears and serve.