In small saucepan, melt butter over medium heat; cook flour, stirring, for 1 minute. Whisk in milk, 2 tbsp (25 mL) at a time, until thickened and smooth; cook over medium-high heat, whisking, until thick enough to mound on spoon, about 2 minutes. Whisk in salt, nutmeg and hot pepper sauce. Scrape into bowl; let cool for 10 minutes.
Meanwhile, pick through crab to remove any cartilage. Add to milk mixture along with 1/2 cup (125 mL) of the bread crumbs, egg, onions and parsley; mix well.
Using damp hands, form into eight 1/2-inch (1 cm) thick patties. Sprinkle remaining bread crumbs onto plate; gently press patties into crumbs, turning to coat. (Make-ahead: Cover and refrigerate for up to 24 hours.)
In nonstick skillet, heat oil over medium heat; fry patties, turning once, until browned and crisp, about 10 minutes.