In the bowl of a food processor, combine flours and salt. Scatter chilled butter over top and pulse until mixture resembles coarse sand and butter pieces are the size of small lentils, about 10 pulses. Continue pulsing, adding water 1 tablespoon at a time until dough begins to form small curds that hold together when pinched, about 10 pulses.

Turn mixture onto a lightly floured surface and gather into a rectangular pile. Use the heel of your hand to smear a small amount of the dough against the counter. Continue this process until all of the dough has been processed. Collect dough into a rectangular pile and repeat smearing process once more. Form dough into a 6-inch disk, wrap with plastic wrap and refrigerate 1 hour (or up to 2 days).

Roll dough into a 12-inch circle between two sheets of parchment paper lightly dusted with flour. Slide dough, still between parchment paper, onto a rimmed baking sheet and refrigerate 15 minutes.

Meanwhile, heat oven to 375ºF with rack set in lower-third.

Toss peach wedges with coconut sugar, 1 tablespoon lime juice, 2 teaspoons lime zest, and cornstarch. Remove the top sheet of parchment from dough. Sprinkle Gouda over dough, leaving a 2-inch border around edge of dough. Layer peach wedges over cheese in a spiral working from the outside towards the center, leaving the 2-inch border around edge of dough. Drizzle any accumulated juices from the bowl over the peaches.

Fold outer 2 inches of dough over filling, pleating dough every 2–3 inches as needed. Gently pinch pleated dough to secure, making sure not to pinch dough into fruit. Brush tart dough with beaten egg then sprinkle dough with almonds and turbinado sugar, if using.

Bake tart until golden brown and peaches are tender, 50–60 minutes. Rotating sheet halfway through baking.

Let tart cool on sheet for 10 minutes. Slide onto a wire rack and cool until juices have thickened, about 20 minutes. Drizzle galette with honey and sprinkle with flaky sea salt and fresh thyme.