I have tried Nigella's Pavlova recipe two times but every time I make it it is pretty flat after baking. The centre is marshmallowy but the top doesn't go crisp. I use the exact measurements though I use distilled vinegar as wine vinegar isn't availabe here, is that the problem? Also I live in a hot country, could this have caused the problem? Please help!
When making meringues make sure that all of your utensils are grease free so that the egg whites whisk properly. Avoid using plastic bowls, as grese tends to stick to them, and to be sure you can wipe the bowl and beaters with a little lemon juice or vinegar to remove any traces of grease. Whisk the whites to firm peaks before adding any sugar as this should give you the best possible volume for your meringue.
The type of vinegar should not matter, it is added as the acid helps to stabilize the whisked egg whites and give a firmer meringue. You can use lemon juice instead of vinegar if you are not sure about the vinegar used.
We suspect the main cause of the problem is a humid environment. When you bake meringues you are mainly drying them out, causing the sugar and egg white to form a crisp shell. Unfortunately in a humid environment the meringue may not dry out fully, and even if it dries in the oven it will start to absorb moisture from the air as soon as it comes out of the oven. This would give a slightly sticky crust and a very soft centre. Sadly there is no remedy for this so you may prefer to explore other desserts instead.