With kitchen shears, carefully cut the hens in half down the center of the breast and along the spine.
Pat the birds dry with paper towels and place them on a baking sheet. With the shears, cut the tips of the wings off and discard.
In a small bowl, combine the melted butter and 2 tablespoons of the whole grain Dijon mustard. Whisk them together then brush the mixture all over the tops of the hens, coating them well.
Bake for 40-45 minutes or until the hens test done with a meat thermometer (165°) or the juices run clear.
While the hens rest, prepare the gravy.
In a saucepan, melt the remaining 2 tablespoons of butter. Whisk in the flour and allow it to cook for just a minute.
Whisk in the half & half. Add in the remaining mustard, salt, & pepper.
Stirring continually, bring this to a gentle boil. Let it cook for one minute and remove from the heat.