Combine the dry ingredients – Add the wholegrain spelt flour, salt, and thyme to a large mixing bowl. Mix with a fork or spatula until the thyme is evenly distributed throughout the flour.
Add the wet ingredients – Add the water, olive oil, and firm soy yogurt. Mix until the ingredients begin coming together into a rough dough. It may look a little uneven at first, which is completely fine.
Bring the dough together – Use your hands to gather the dough, scraping up any flour remaining at the bottom and sides of the bowl. Continue until you have one cohesive piece of dough.
Knead the dough – Lightly flour your work surface and transfer the dough onto it. Using the fingers of your dominant hand, press down on the edge of the dough closest to you, while using the heel of your other hand to stretch the dough forward from the center. Roll it back, turn it 90 degrees, and repeat. You can also knead it using another technique that feels more comfortable—the important part is to work the dough enough to develop the gluten.
Shape the dough – Once the dough feels smoother and more elastic, shape it into a ball. You don't need to knead it for a long time; the goal is simply to bring the dough together and develop enough gluten for it to roll out easily.
Roll out the dough – Add a medium-to-generous amount of flour to your work surface and lightly flour both the dough and rolling pin. Roll the dough out, continuously rotating and moving it so it doesn't stick and gradually forms a rough circle. You can make the edges slightly thinner than the center.Aim for the right thickness – Roll the dough to approximately 0.5 cm (¼ inch) thick. If the dough feels too sticky to handle, place it between two sheets of lightly floured parchment paper and continue rolling. Use immediately or fill – The dough is now ready to fill and bake. For a savory version, try it with roasted vegetables, mushrooms, creamy sauces, or cheese alternatives. For a sweet galette, omit the thyme and fill it with fruit or another sweet filling.