01 -
Whisk the balsamic vinegar, honey, whole grain mustard, garlic, salt, and pepper in a large bowl until combined.
02 -
Add the sirloin cubes and toss until coated. Cover and refrigerate for at least 20 minutes, or up to 8 hours for deeper flavor.
03 -
In a separate bowl, toss the grape tomatoes with olive oil and chopped rosemary. Let them sit at room temperature while you cook the potatoes.
04 -
Place the baby potatoes in a saucepan and cover with water by 1 inch. Bring to a boil and cook for 8-10 minutes, until barely fork-tender. Drain and cool slightly.
05 -
Thread each skewer with potato, steak, and tomato, repeating the pattern and leaving a small space between pieces. Do not pack the skewers tightly.
06 -
Heat a grill to medium and oil the grates. Grill the kebabs for about 5 minutes per side, turning once, until the steak is browned and cooked to your preferred doneness.
07 -
Transfer the kebabs to a platter and rest for 5 minutes before serving. Spoon any juices from the platter over the top.