To make the chocolate cookie crust:

1. Adjust oven rack to lower middle position. Pre-heat oven to 350 degrees F.
2. Pulse the chocolate animal crackers in a food processor until crumbs are formed. Pour crumbs into a bowl. Stir in melted butter and sugar. The mixture should be sandy. 
3. Pour mixture into a 9-inch springform pan. Use the bottom of a glass or a measuring cup to pack the mixture down firmly on the bottom and sides of the pan. 
4. Pre-bake the crust for 8 to 10 minutes. Remove the crust from the oven and let it cool completely.

To make the chocolate cheesecake:

1. Combine chocolate chips and milk in a microwaveable bowl. Heat in 30 second increments in the microwave.  Stir frequently until the chips melt and the mixture is smooth.  Then stir in the espresso powder.  Set aside.
2. In a stand mixer fitted with the paddle attachment, beat room temperature cream cheese and sugar together on medium-low speed until thoroughly combined. Scrape down the sides of the mixer bowl.
3. Add the eggs one at a time. Beat after each egg until just combined. Do not over-mix.
4. Stir in the vanilla and the flour. Add the chocolate mixture, and beat on low until combined. Scrape down the sides of the bowl.
5. Prepare the water bath. Wrap your springform pan in heavy duty aluminum foil. Make sure it is wrapped on the bottom and all the way around the pan.  Boil enough boiling water to go up at least an inch to halfway up the side of your springform pan.  
6. Pour the chocolate cheesecake filling into the prepared springform pan. Tap it a couple times on the counter to make sure that the surface is flat and to remove any air bubbles. 
7. Place the springform pan into a roasting pan. Carefully pour the boiling water into the roasting pan in a slow and steady stream. Try to avoid splashing it into the springform pan.  Place entire roasting pan in the oven. 
8. Bake the cheesecake for 45 to 55 minutes, until the center is almost set.  If using a digital thermometer, the cheesecake should be cooked to about 175 degrees F. 
9. Turn off the oven. Crack the oven door open about an inch, and allow the cheesecake to cool in the warm oven for an hour. Then remove the roasting pan from the oven. Take the cheesecake out of the roasting pan, and allow it to cool to room temperature. 
10. When it is completely cooled, you can add the mousse topping.  

To make the espresso mousse topping: 

1. Stir egg yolks and sugar until the mixture is creamy and pale yellow.
2. Stir in cornstarch. Gradually whisk in the warm milk until it is completely combined.
3. Place the yolk mixture into a small saucepan, and cook over low heat. Bring to a boil, stirring continuously until the mixture is thickened.
4. Remove from heat. Stir in vanilla extract and espresso powder. Allow the mixture to cool.
5. Meanwhile in another small saucepan, dissolve 1/2 tablespoon of gelatin powder into 2 tablespoons of water.  Allow this to “bloom” or swell for 5 to 10 minutes.  
6. Place saucepan with gelatin over low heat just until the gelatin dissolves. Remove from heat.
7. Pour gelatin into espresso mixture, and stir to combine.
8. In a chilled bowl, beat 1 cup of chilled** whipping cream until stiff peaks form. Gradually fold whipped cream into coffee mixture.  Do not over mix, or the mousse will deflate.

To assemble:

1. Once the mousse is mixed, immediately spread it over the cooled/chilled cheesecake.  Depending on the depth of your cheesecake pan, you may have more mousse than you need. Use an offset spatula to smooth the mousse.
2. Cover cheesecake and refrigerate at least 4 hours or overnight.
3. Take a knife, and run hot water over it. Use the knife to release the cheesecake from the edges of the pan before removing the springform ring.
4. Dust the cheesecake with cocoa powder, and garnish with berries and chocolate shavings.