Try using a fine mulch rather than soil for blanching - less sand to wash out when you're using them, and all that's needed for blanching is to exclude light.
Also I grew up loving leeks, especially in my great-aunt's torta - an Italian flat sort of pie. Sliced leeks with savoy cabbage (more cabbage than leeks), a light dressing of olive oil, a sprinkle of flour to absorb released moisture, black pepper and grated parmesan cheese. Add a little salt if needed. Use a light hand throughout - let the vegetables shine through. Fill a simple pastry shell (not too rich, please, and not too thick a layer of filling. Think quiche.), cover with top pastry, fold over selvage of bottom crust, don't crimp a raised rim, cut vents for steam, bake in a fairly hot oven (425 a good place to start). Turn out of the pan, let cool until warm, cut and enjoy. Delicious at room temperature too.