Drain the crab meat very well (removing as much liquid as possible) and place in a medium size bowl. Add the cream cheese, horseradish and lemon juice and mix until evenly combined. Stir in the onion, tarragon, salt and pepper. Taste and adjust the seasoning as you like. Place in a serving bowl and cover with plastic wrap. Chill in the fridge until ready to serve. Also tastes great the day after it is made and the flavors have had time to combine.