Step 1Combine the flour, salt and butter in a food processor and pulse until a crumbly dough forms. Add the ice water to the dough and continue pulsing until well mixed. Form the dough into a ball, wrap securely in plastic wrap and refrigerate until firm, about 2 hours. (At this point the dough can be placed in a sealed plastic bag and frozen for up to one month. To use, place in the refrigerator for 2 hours to thaw before baking.)
Step 2Heat the oven to 400 degrees. Take half the dough from the refrigerator, transfer it to a flat, floured surface and roll it out to a one-eighth-inch thickness. With a small glass or a cookie cutter, cut circles that are slightly larger than the 2-inch tartlet molds. Press each circle into a mold and pinch off any excess. Pierce the bottom and sides of each shell several times with a fork and put them in the freezer for 10 minutes to re-chill the dough.
Step 3When the dough is firm again, bake the shells for 15 to 16 minutes, until they are very light golden. Cool on wire racks before carefully turning out of the molds.
Step 4Repeat the rolling out, molding and baking process with the remaining dough. At this point the shells are ready to be filled or they may be transferred to an airtight container and refrigerated for up to 1 week or frozen for up to 1 month.
Step 1Squeeze excess water from the spinach, then chop finely or puree; set aside.
Step 2In a saucepan over low heat, whisk together the miso, mirin, vinegar, salt, sugar and water until a smooth sauce forms. Remove the mixture from the heat, add the spinach and toss to combine. Stir in the eggs and cream.
Step 3Reduce the oven heat to 350 degrees. Spoon a scant 1 tablespoon of filling into each shell. Transfer the filled shells to a baking sheet, cover gently with foil and bake for 15 minutes or until the mixture has set. Remove the foil, bake for 2 minutes longer, then serve.