Sirloin flap is a beautifully marbled cut of meat that comes from the bottom part of the sirloin butt. This somewhat unrecognized cut is known as bavette, or is sliced and presented as sirloin tips. It is similar to the flank and skirt cuts, but is suppler and much beefier. Whether you sous vide and finish with a quick sear or marinate and then grill the meat, make sure to slice your sirloin flap across the grain.