Preheat the oven to 300°F. Grease an 8-inch round pan.

In a small bowl, combine the cookie crumbs and 3 tbs. of the sugar. Stir to mix well. Pour in the melted butter and toss together to moisten evenly. Dump the crumb mixture into the prepared pan and press to cover the bottom and 3/4 of the way up the sides.

To make the filling, place the cream cheese, 2⁄3 cup of the remaining sugar, the banana, sour cream and flour in a food processor; pulse to form a smooth paste. With the machine on, add the eggs, one at a time; scrape down the bowl and pulse briefly.

Measure out 1¼ cups of the cream cheese filling and set it aside. Scrape the remaining filling into the prepared pan. Return 1 cup of the reserved filling to the food processor. Add the melted chocolate and combine, scraping the sides of the bowl well to make sure the batter is evenly mixed. Drizzle the chocolate filling in an abstract ribbon pattern over the top of the cream cheese filling in the pan. Drizzle the remaining ¼ cup banana filling over the chocolate and use a blunt knife or bamboo skewer to swirl them into a marbled pattern; do not overmix.

Bake in the center of the oven for 45 minutes. Remove the cake from the oven and run a knife all the way around the edges to release the cake and crust. Return the cheesecake to the oven, turn off the heat, and let stand without opening the door for 15 minutes. Remove the cake from the oven and let stand in the pan on a rack until cooled to room temperature. Cover and refrigerate the cake for at least 3 hours, or preferably overnight, to set completely.

To remove the cake from the pan, wrap a flat plate or tray with plastic wrap and spray it lightly with nonstick cooking spray. Hold the bottom of the cake pan over low heat until it is slightly warm but not hot. Gently shake the pan from side to side to release the cheesecake. Place the greased plate over the top of the cake and quickly invert it. The cake should slide right out of the pan. Place your serving plate on the bottom of the cake and invert it again right side up.

For the strawberry sauce, place the strawberries and remaining 3 tablespoons sugar in a blender or food processor and puree until smooth.

To cut the cake, use a large chef’s knife dipped in hot water and wiped clean between cuts. Serve each slice with a drizzle of strawberry sauce. Top with a garnish of whipped cream and chopped walnuts.