Prepare spiral ham according to package directions. I serve mine room temperature.
Combine brown sugar and water in small saucepan and heat over medium heat until brown sugar is dissolved. Heat until it reaches a low boil, approx. 5 minutes.
Stir in mustard and simmer for 2-3 minutes.
Stir in butter until melted.
Serve glaze/sauce with ham (or corned beef).
If leftover glaze (refrigerated) becomes too thick, simply heat in microwave for 10-15 seconds.