A pat of the slightly tangy butter is tucked into the center of each beef patty. As the burger cooks, the butter melts, giving the meat an extra-tender texture and a hit of citrusy flavor. For step-by-step photos of this recipe, see our tips on how to stuff a burger.
6 tablespoons (3/4 stick) butter, room temperature
1 tablespoon finely chopped fresh tarragon
1 tablespoon finely chopped fresh basil
1 tablespoon finely chopped fresh Italian parsley
1 teaspoon finely grated Meyer lemon peel or regular lemon peel
1 teaspoon fresh Meyer lemon juice or regular lemon juice
1 1/2 pounds ground beef (15% fat)
Vegetable oil (for brushing)
4 sesame seed hamburger buns
1 large tomato, thinly sliced crosswise
1 bunch arugula
Meyer lemons are a bit sweeter than regular lemons and have a slight floral notes. They’re available at some supermarkets and farmers’ markets.
Mix butter, all herbs, lemon peel, and lemon juice in small bowl. Season with salt and pepper. Measure 1/3 cup herb butter; transfer to sheet of plastic wrap (reserve remaining butter in bowl for spreading on buns). Using plastic wrap as aid, form butter into 3-inch-long log; wrap plastic around to seal. Freeze until firm, about 30 minutes. Cut crosswise into 4 rounds. Flatten rounds into 2-inch-diameter disks.
Divide meat into 4 equal pieces. Using damp hands, form each piece into ball. Using thumb, make deep wide indentation in center of each ball. Press 1 lemon-butter round flatly into indentation, then press meat securely over butter to enclose. Flatten each burger into 3 1/2-inch-diameter patty, leaving butter rounds horizontally in center of each burger. DO AHEAD Herb butter and burgers can be made 6 hours ahead. Place burgers on baking sheet, cover with plastic wrap, and chill. Cover and chill herb butter in bowl; bring to room temperature before continuing.
Brush barbecue rack with oil. Prepare barbecue (high heat). Sprinkle both sides of burgers with salt and pepper. Spread remaining butter over cut sides of buns. Grill burgers until cooked through, 4 to 6 minutes per side. Grill buns until slightly charred, about 1 minute per side.
Place burgers on bun bottoms. Top with tomato slices and arugula leaves. Cover with bun tops and serve.