Fill large saucepan with water and bring to a boil. Add the beans to the water, and blanch for 3 to 4 minutes, until they are pliable but still crunchy. Drain, run under cold water and pat dry.
In a medium saucepan, melt the butter. Stir in the dry mustard, brown sugar, garlic, and salt. Pour the butter mixture over the green beans to coat. Refrigerate, covered, at least 4 hours or overnight.
Preheat oven to 375 degrees.
Make bundles of about 8 beans each. Wrap half a bacon slice around each bundle, secure with a toothpick and arrange in a single layer in a casserole dish.
Bake, uncovered, for 45 minutes, or until bacon is cooked and beans look wrinkled. Remove from oven and warm or at room temperature. Pour off some of the butter before serving.