Crush the biscuits into crumbs, mix with brown sugar, vanilla extract and melted butter. Mix very well, the mixture will turn out in consistency, like wet sand.

Wrap a detachable form (22-23 cm) on the outside with foil in several layers so that water does not get inside (when baking in a water bath). Grease the inside of the mold with oil. Spread the crumb mixture evenly across the bottom of the pan, pressing it against the bottom and halfway down the sides.

Break or cut the chocolate into small pieces, evenly distribute it on the base, spread the marshmallows on top (if it is large, you can cut it with wet scissors).

In a bowl, mix soft cream cheese, cornstarch, vanilla extract, sour cream and sugar, pour in the cream. Beat at low speed with a mixer.

Add eggs one at a time, beating with a whisk. If the mixture turns out to be watery, you can add a spoonful of sour cream thickener and beat the mixture.

Pour the batter into the pan and spread evenly with a spatula.

Place the cheesecake pan in a large baking pan. Carefully pour boiling water into a large mold, approximately to the middle of the mold wall. Bake 90-95 minutes. Turn off the oven and open the oven door half way. Let cheesecake rest 10 minutes and remove from oven.

Gently run a butter knife between the sides of the cheesecake and the springform pan to gently separate it from the pan. Don't take the cheesecake out of the mold yet. Refrigerate the cheesecake for an hour.

Turn on the roaster in the oven. Cover the top of the cheesecake with melted chocolate.

And spread the marshmallows evenly.

Place the cheesecake in the oven, under the roasting pan. Let the marshmallows roast for only 30-35 seconds. It fries up very quickly. If there is no roaster, then turn on the oven at 200C and leave the cheesecake for 2-3 minutes to roast the marshmallows on top. Remove the cheesecake as soon as the marshmallow is lightly browned. Cool the cheesecake completely, cover carefully and refrigerate for at least 4 hours. Cut with a wet knife.