Preheat oven to 350°F Liberally butter a 9 inch springform pan, then wrap the base in heavy-duty foil. Set a kettle on to boil.
In a small bowl, mix the crushed chocolate cookies, butter, 2 tablespoons sugar, and cocoa until well moistened. Press into the bottom of the prepared springform pan; use a glass or measuring cup to pack the crust down firmly.
Place the cream cheese in a large bowl (or the work bowl of a stand mixer) and beat with an electric mixer set to low speed until smooth. Slowly add 1 cup sugar, then the eggs, one at a time. Continue beating until smooth.
Combine the chocolate chips and heavy 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. Place the pan on the middle rack of your oven. Fill the dish with boiling water halfway up the side of the springform pan.
Bake the cheesecake in the water bath in the preheated oven for 45 minutes. Turn oven off, leaving the cheesecake in the oven with oven door slightly ajar another 45 minutes; remove from oven. Run a thin knife along the edge of the cheesecake to loosen from pan. Chill in refrigerator at least 4 hours.
Melt the semisweet chocolate in a small bowl using the microwave (stir every 20 seconds until fully melted). Make chocolate clovers by dropping 3 small drops of melted chocolate close to one another on waxed 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.