Cut butter into small pieces. Finely chop dark chocolate and transfer to a large bowl (large enough for all ingredients). Heat up Baileys in a small saucepan over medium heat for approximately 2 min. Add instant espresso and mix until dissolved. Carefully pour warm Baileys/Espresso mix into bowl, melting the chocolate. Once chocolate is melted, add butter slowly, and stir through until well combined. Fill cream into piping bag and chill for approximately 30 mins.