Set aside 2 tbsp (30 mL) of the parsley. In food processor, pulse together remaining parsley, onions, mushrooms and garlic until minced; transfer to bowl. Add beef, egg yolk and 3/4 tsp (4 mL) each salt and pepper; mix well. Form into 8 patties.

Place flour on plate; coat patties with flour on both sides. In large cast-iron or nonstick skillet, heat 1 tbsp (15 mL) oil over medium heat; fry patties, turning once, until digital thermometer inserted sideways into centre reads 160°F (71°C), 15 to 18 minutes. Transfer to paper towel–lined plate to drain off fat; transfer to serving platter.

Meanwhile, cut tomatoes in half crosswise. In skillet over medium heat, heat 2 tbsp (30 mL) oil; place tomatoes in skillet, skin side down, and sprinkle with 1/4 tsp (1 mL) salt. Cover and fry until tender, 10 to 12 minutes. Top patties with tomatoes and pan juices; mince remaining parsley and sprinkle over top.

Makes 6 servings.