I added the sugar and horseradish mustard after I had it all mixed up, so there ain't picture of that for you. Sorry.
Here it is all mixed up and ready to go sit in the fridge.
1 T. prepared horseradish
1 T. prepared regular mustard
2 T. brown sugar
2 tsp. horseradish mustard
Combine everything in a small bowl and refrigerate. Serve with corned beef.