Add the cubed butter and with clean, dry hands, cover the cubes of butter with flour. Then pinch the butter into the flour, flattening the butter and making very rough and coarse crumbs. You want to keep the butter mixer cold as you are doing this. If the mixture gets too sticky, put it in the freezer for a couple of minutes.
Add the sourdough discard to the butter mixture. Using a mixing spoon, combine the wet starter into the butter/flour mixture. Stir only to combine.
Lay a piece of parchment paper onto your counter and dump the dough onto the parchment and work it into a round thick disc.
Fold up the parchment around the disc, and chill it in the fridge for a minimum of 30 minutes.
Pre-Roast the Asparagus:
Toss the asparagus in olive oil, sprinkle with sea salt and roast at 375°F (190°C) on a parchment lined baking sheet for 10 minutes.
Pre-bake the Crust:
Preheat the oven to 375°F (190°C).
Roll out the dough to ⅛ inch thick on its piece of parchment to the size of your 9 inch tart pan, baking pan, or shape it rustic style on a baking sheet. If the dough gets sticky during this process, just put it in the freezer on its parchment for a few minutes.
Poke the finished crust with a fork and blind bake for 10 minutes with pie weights.
Prepare the Filling:
In a bowl, mix goat cheese, cream, eggs, lemon zest, dill, garlic, thyme, salt, and pepper, until smooth.
Spread the mixture over the parbaked crust.
Arrange asparagus on top. Sprinkle with fresh ground black pepper and Parmesan, if using.
Bake & Serve:
Bake at 375°F for 25-30 minutes until set and golden.
Let cool slightly before slicing. Serve warm or room temp. Garnish with fresh dill fronds if desired.
Notes
Keeping the crust flaky: Ensure the butter remains cold while mixing to achieve a flaky crust. If it starts to soften, chill the dough briefly before rolling.Make it ahead: The crust can be prepared a day in advance and kept chilled. The tart can also be assembled and refrigerated overnight before baking.Cheese substitutions: If goat cheese isn’t available, try cream cheese, ricotta, or feta for a different but complementary taste. (These have not been tested)Store leftover tart covered in the refrigerator for up to 3 days. Reheat slices in the oven at 300°F until warmed through, or enjoy cold straight from the fridge.To freeze, wrap individual slices in plastic wrap and place in a freezer-safe container. Thaw in the fridge overnight and reheat before serving.