Preheat oven to 350ºF. Line a 9x13” baking pan with parchment paper, or grease well.
Beat butter with sugar in standing mixer until light and fluffy, about 3 minutes. Beat in eggs, one at a time, beating well after each to incorporate. Beat in vanilla extract and cooled chocolate.
In a separate bowl, whisk together flour, cocoa and salt. With mixer speed on low, gradually incorporate dry ingredients into chocolate mixture. Scrape into prepared pan and bake about 30 minutes, or until centre is set. Cool completely on a wire rack.
To make frosting:
Beat butter and sugar until light and fluffy, about 3 minutes. Beat in peppermint and vanilla extracts. Spread frosting over cooled brownies and sprinkle with crushed candy canes