To my knowledge Nigella Lawson is not really considered a pastry chef. Pastry chefs primarily concentrate on making such things such as cakes, cookies, cupcakes, pies, tortes and ice cream and sometimes bread. Certainly Lawson does make these “pastries” but she makes lots of other things too. She will often suggest and even provide recipes for yummy desserts to go along with a meal but she is not really a pastry chef.
The general public would probably not really recognize the names of most pastry chefs, for example, have you ever heard of “the Picasso of Pastry”? This is a name used for the French pastry chef Pierre Hermé.