OK, I'm making lemon tarts and I need some info on lemon curd! 3 questions:

1) What is the difference between lemon curd and the lemon filling (i.e. lemon meringue pie filling)? Apart from the pie filling having starch, is there any?

2) When preparing lemon curd, is it better to use a double boiler or in a single pan directly over heat?

3) Lemon tarts havealways been a favorite of mine, not only for their taste but for their look! I would love to know how to "dome" the lemon filling/curd on my tarts. (Does this make sense?)

Be patient with me -- I'm a beginning baker! Thanks!