Lettuce Burger With Feta Cheese & Pesto

INGREDIENTS: 3 oz. ground beef, 2 tbsp. red onion, 1 tsp. basil pesto,  ½ tsp. garlic,  2 slices tomato,  ¼ tsp. ground cumin,  1 tbsp. feta cheese,  ½ tbsp. butter, 1 tbsp. sour cream, 1 large lettuce leaf 

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