Cherry Compote
Put all ingredients in a small saucepan and bring to a simmer. (If you're using frozen cherries, there's no need to thaw the cherries before adding to the pan.)
Simmer for about 20 minutes, until juices are thick and syrupy, and coat the back of a spoon. Stir the mixture regularly to avoid burning
Cool completely before using it.
Cookie Crust
In a food processor, pulse the Oreos into a very fine crumb. (You can also crush the Oreos in a Ziploc bag with a rolling pin.)
Use a fork to mix the cookie crumbs and the melted butter until the mixture is evenly mixed and resembles wet sand.
Press mixture into a 14 x 4.25-inch rectangular tart pan. Use a tamper tool, the flat bottom of a ¼ cup measuring cup, or the bottom of a small glass to firmly press into the bottom and sides of the tart pan. The crust should come up the sides of the tart pan.
Bake in a preheated 350° oven 6 minutes. Let cool completely before adding the filling.
Chocolate Ganache(Ganache will be divided, ½ cup for spreading on the bottom of the tart. The remainder is mixed with whipped cream for the filling.)
Place chocolate chips in a small bowl, set aside.
Bring heavy cream to just about a boil. Pour heavy cream over the chocolate chips. Let sit for 60 seconds.
Gently whisk the chocolate and heavy cream until the chocolate is melted and smooth.
Let cool completely at room temperature before using it. Avoid refrigerate the ganache, which can cause the chocolate to seize.
Spread ½ cup of ganache on the bottom of the tart crust.
Optional: Place an additional 8 sliced and pitted cherries evenly on the bottom of the tart. (place them face side down to keep the juices contained.)
Whipped Cream(Whipped cream will be divided, 1 cup for the topping and the remaining for the filling.)
Pour cold heavy whipping cream into mixing bowl. Add the sugar.
Using the whisk attachment, mix on medium-high speed until light and fluffy and soft peaks form. Remove 1 cup of whipped topping to a small bowl and refrigerate until decorating tart.
Whipped Ganache Filling
Add the remaining chocolate ganache to the remaining whipped cream in a mixing bowl. Mix on low speed until completely combined.
Pour into the tart shell and spread evenly. Refrigerate for 30 minutes minimum.
Chocolate Shavings
Hold a chocolate bar firmly in one hand and using a vegetable peeler peel the edge of the chocolate bar to create shavings.
Decorating
Once the tart is chilled spread the remaining whipped cream on top of the whipped ganache filling.
Gently add the cherry compote on top of the whipped cream.
Sprinkle with chocolate shavings.
If using fresh cherries, place fresh stemmed cherries on top of the tart.
Chill for 20 minutes minimum before serving.
Store leftovers in an airtight container.