I have a 1 gallon blackberry mead going right now, it's about 2.5 months old now and is tasting amazing, it's also the only blackberry mead I've ever made.
The recipe came from stormthecastle.com
1 package of Red Star "Premier Cuvee" yeast
4 pounds of clover honey
1 gallon of spring water
8 ounces of Black berries - Frozen
1 whole clove
inch and a quarter ( 1 1/4 ) long section of a vanilla bean. Split length-wise.
Tossed everything but the vanilla bean into the primary and let it ferment til if finished, then racked to secondary and tossed in the split vanilla bean. Still sitting on the vanilla bean, and it still has a wee bit of an alcohol taste to it yet, but if this turns out as well as I think it's going to I will definitely be making a 5 gallon batch of it
Note I used the whole vanilla bean, which was probably about 3 inches long.