Put the beef in a medium bowl. Grind the ginger slices with a mortar and pestle, adding them a few at a time until you have extracted most of the juice, or use a mini-chop to make a wet paste. Squeeze the juice from the fibers (you should have 1 1/2 to 2 tablespoons) and stir it into the beef; discard the ginger solids. Let the beef marinate for at least 10 minutes.
Meanwhile, make the paste: Blend all the ingredients in a blender until smooth, 2 to 3 minutes.
Heat the oil in a large pot over medium-high heat. Add the paste and cook, stirring occasionally, until the flavors are released, about 2 minutes. Stir in the beef, sugar, fish sauce, soy sauce, salt, pepper and broth. Bring to a boil, reduce the heat to low and simmer, partially covered, until the liquid is reduced by half, about 40 minutes.
Add the coconut and tamarind juices and cook for another 20 minutes. If the sauce is too thin at this point, increase the heat and reduce further; the sauce should be fairly thick.
Garnish with cilantro sprigs and serve with cucumber slices and rice.