Preparation Puree blackberries, raspberries, and lime juice in blender until smooth. Strain through fine mesh strainer into large measuring cup. Add sugar; stir until dissolved. Refrigerate berry puree at least 1 hour and up to 1 day. Mix tequila and Grand Marnier into berry puree. Transfer half of mixture to blender; add half of frozen strawberries and 2 1/2 cups ice. Blend until smooth. Transfer to pitcher. Repeat with remaining berry puree, frozen strawberries, and ice. Pour into sugar-rimmed Margarita glasses and serve.
Preparation Puree blackberries, raspberries, and lime juice in blender until smooth. Strain through fine mesh strainer into large measuring cup. Add sugar; stir until dissolved. Refrigerate berry puree at least 1 hour and up to 1 day. Mix tequila and Grand Marnier into berry puree. Transfer half of mixture to blender; add half of frozen strawberries and 2 1/2 cups ice. Blend until smooth. Transfer to pitcher. Repeat with remaining berry puree, frozen strawberries, and ice. Pour into sugar-rimmed Margarita glasses and serve.