Ethiopian Spiced Steak

Name: Ethiopian Spiced Steak
Ingredients: One 1 1/2-pound sirloin steak; 1 1/2 tablespoons berbere spice (see Note); 1 pint red cherry tomatoes, halved; 1 pint yellow cherry tomatoes, halved; 2 tablespoons extra-virgin olive oil; Salt and freshly ground black pepper; 2 tablespoons fresh lemon juice; 3 large celery ribs, thinly sliced, plus 1/2 cup leaves; 2 tablespoons chopped parsley; 2 tablespoons capers, drained and chopped; 2 teaspoons red wine vinegar; 1/2 red onion, thinly sliced; 4 tablespoons unsalted butter; 3 cups vegetable oil; 1 large baking potato—peeled, cut into 3-by- 1/4-inch sticks, rinsed and dried completely; 1 head Boston or green leaf lettuce, separated into leaves