In the top of a double boiler
, whisk the sugar and the egg yolks until sugar has dissolved and mixture is pale yellow, then whisk
in lemon juice and zest. Set the bowl over simmering water and whisk constantly until mixture reaches 145 degrees F; it will visibly thicken but don't let it get too hot or the eggs
. Remove the bowl from the heat and add the rosemary and butter a little at a time, whisking until each addition is incorporated and the curd becomes thick. Transfer to a bowl, cool and then refrigerate until well chilled.
Divide the berries among 6 decorative bowls or glasses. Top with a dollop of the lemon curd and sprinkle with biscotti crumbs.