Preheat oven to 180 degrees C. Prepare a 20cm springform pan with butter.
Combine the crushed biscuits, butter, 2 tablespoons sugar and cocoa in a small bowl; mix; press into the bottom of the prepared springform pan.
Place the cream cheese in a large bowl and beat with an electric mixer set to low speed until smooth. While beating slowly add 1 cup sugar and then the eggs, one at a time. Continue beating until smooth.
Combine the chocolate chips and cream in a microwave-safe bowl. Heat in the microwave until the chocolate is completely melted, stirring every 30 seconds. Beat the chocolate into the cream cheese mixture.
Add the sour cream, salt, beer and vanilla; blend until smooth. Pour the mixture over the crust. Place the pan into a large deep baking dish. Fill the dish with water to cover the bottom half of the springform pan.
Bake the cheesecake in the water bath in the preheated oven for 45 minutes; turn oven off; leave the cheesecake in the oven with oven door slightly ajar another 45 minutes; remove from oven. Run a knife along the edge of the cheesecake to loosen from pan. Chill in refrigerator at least 4 hours.
Melt the cooking chocolate in a small bowl using the microwave. Make chocolate clovers by dropping 3 small drops of melted chocolate close to one another on greaseproof paper. Drag a toothpick from between two dots outward to make the stem; chill until hardened. Arrange the chocolate clovers on top of the chilled cheesecake for decoration.