Place tapioca flour, cornstarch, sweet rice flour, millet flour, salt, guar gum and sugar in the bowl of a stand mixer fitted with the paddle attachment. Beat lightly to combine. Add the butter, and mix on medium speed until the mixture becomes pebbly. Add the eggs and beat just until the mixture turns on itself. Turn out onto a board that’s been lightly floured with tapioca flour and knead for one or two turns. Flatten dough into a disk, wrap in plastic and refrigerate for at least 2 hours (it can be stored for a few days in the fridge).
Lightly flour a board with tapioca flour. Turn out the dough onto the board, and roll to a ¼ inch thickness. Cut the dough into rings using a small glass or jar (about 3 inches in diameter). Press the rings into the cups of the muffin tins so that the dough goes up about half way. Put the tins in the freezer for 30 minutes.
Preheat the oven to 375 degrees. Prick the frozen tart shells with a fork, place in the oven and bake for about 15-20 minutes, or until the tart crust is golden brown. Remove from the oven and using a spoon, press any air bubbles out of the crusts. Let cool for 10 minutes, then carefully lift out of the tins onto a cooling rack.
Lemon Curd
Remove the zest from the lemons using a vegetable peeler, taking care to use only the yellow part of the peel, not the white pith. Place into the bowl of a food processor fitted with a steel blade attachment. Add the sugar and lavender and pulse until the zest is chopped into tiny bits and thoroughly combined with the sugar. Add the butter and pulse until smooth. Add the eggs, one at a time and pulse until smooth. Add the lemon juice and salt and pulse again.
Pour the mixture into a medium saucepan set over low heat. Cook for 10-15 minutes, stirring constantly, until the mixture is quite thick…like a soft-set pudding.
Pour the mixture through a sieve into a bowl or pitcher, straining out any bits of zest or lavender.
Pour the warm curd into the cooled tart shells and set aside.
Meringue
Whip the egg whites, cream of tartar, and ¼ teaspoon salt in the bowl of an electric mixer fitted with the whisk attachment on high speed until frothy. With the mixer still running, slowly add the sugar and beat until the meringue is thick and shiny, about 2 minutes.
Spoon the meringue into a large piping bag fit with an open star tip. Pipe the meringue decoratively over the cooled tarts. (Alternatively, spoon the meringue over the tarts). Put the tarts on a pan and under a hot broiler for 30 seconds to lightly brown the tops–WATCH CAREFULLY (or use a small kitchen blow torch like we did).
Notes
Look for culinary lavender in gourmet shops, or find it online.