Cream together the butter and sugar, then add the egg yolk, lemon juice and lemon zest (if using) and stir to combine. Then add the flour, arrowroot, calendula, thyme, and salt.
Gently stir everything together until the dough barely holds together. It will seem a bit floury, but that’s ok.
Take the dough out of the bowl and form it into a log shape.
Wrap it tightly with parchment paper, twisting the ends to help hold it all together.
Put in the fridge or freezer for about 30 minutes, or until firm. You can store the dough for several days in the fridge, or for several weeks in the freezer, if need be.
When ready to cook, preheat the oven to 300°F. Slice the log into 1/4 inch rounds.
Put them on a parchment lined baking sheet, about an inch or so apart. They don’t really spread much.
Bake for 25-30 minutes. Check them closely after 25 minutes, as they will start to brown pretty quickly. Take them out when only the edges just barely start to turn golden. The centers will still be fairly soft. Let them cool on the baking sheet for several minutes before transferring them to a cooling rack. They will firm up as they cool.
Notes
Alternate choices of herbs and flowers: Nasturtiums, violets, borage, lavender basil, oregano, and sage would all work beautifully.