1) Slice bread lengthwise, scoop out a portion of the middle to form a trench and brown under broiler. Set aside. 
2) Melt butter in olive oil and add onion when it begins to brown. 
3) Sautee until translucent and then add seeds, rosemary, and mustard. 
4) When seeds are fragrant, drain the liquid from the salmon can into the onions. 
5) Continue to cook until almost dry and then add cream. 
6) Bring mixture to a boil and then reduce to a simmer until volume has reduced by 2/3.
7) Take sauce off heat and allow to cool for a few minutes. 
8) Mix sauce into salmon, breaking up chiunks as you go and achieving a uniform consistency. 
9) Pile salmon mixture on bread, filling trenches. Arrange on a baking sheet. 
10) Either freshly grate or sprinkle cheese over salmon and place under broiler for 5 to 6 minutes or until cheese is browned. Keep an eye on it incase your broiler runs hot or if you need to rotate.