A “rich” dough has cream and egg yolks added in. This means it can take longer for the dough to knead and will still be quite sticky before its first rise. Not to worry, the dough will lose much of that stickiness as it rises. It’s better to deal with some stickiness than to add too much additional flour and ended up with dense doughnuts. Rich doughs can also take longer to rise, so be sure to give yourself plenty of time!