There’s an infinite number of variables that make for a good time, but on Sunday night, we found the ultimate prescription. We took two sisters and all their beautiful harmonies, tossed in a heavy dose of the Blues, sprinkled in songs from their entire career and mixed them all together in the best cauldron Kentucky has to offer in the Mountain Arts Center in Prestonsburg. Rebecca and Megan Lovell are a blues-oriented, Grammy-nominated duo known as Larkin Poe. Natives of Georgia, now based in Nashville, these young ladies made their way to Prestonsburg armed with an abundance of musical ammunition in reserve. Eager to travel and share their music with…