Fans of the deep-yellow, grass-fed butter from Pastureland dairy co-op have had a tough spring. At several of the Twin Cities dairy cases where it’s usually found – from Seward Co-op to Whole Foods – a big gaping hole has replaced its one-pound packages for the past month. Who knows how many plans for fettuccine alfredo and pound cake and rent-a-movie-night popcorn have had to be shelved for lack of their star ingredient.