Make the crust:
In a large bowl whisk the all-purpose flour, buckwheat flour, sugar and salt until fully combined. Set aside.
In a medium bowl, whisk the skyr and canola oil until combined. The mixture will look curdled and separate but that’s okay, just mix it until they are mixed.
Make a well in the dry ingredients and gently stream in the skyr oil mixture. Using a fork slowly incorporate a little bit of the dry mixture until a shaggy dough begins to form.
Once the dough begins to look shaggy, put the fork aside and use your hands to combine the dough. If the dough is too shaggy and not coming together add a sprinkle of cold water a little bit of a time just until it starts coming together.
Shape the dough into a 1 inch disk and wrap it in plastic. Let the dough chill for 2 hours in the fridge.
Make the filling:
Heat up a large pan to medium heat and add canola oil.
Add the chopped mushrooms and cook until 80% of the water has been released. At that point season with salt and black pepper. Finish cooking the mushrooms for a few more minutes until they begin to look brown and no more water is released. Remove the mushrooms from the pan and place them in a bowl.
Add the remaining canola oil and add the chopped leeks. Let the leeks cook down for 5-10 minutes or until they begin to wilt and start to soften. At that point add the chopped garlic, cooked mushrooms, thyme leaves, salt and pepper. Mix everything together and cook for another 5 minutes until the leeks begin to turn golden and caramelize. Once the mixture is caramelized and slightly golden on the edges transfer the mixture to a bowl and let it cool.
Preheat the oven to 375 degrees. Once the dough has rested, gently roll it out with a rolling pin on a piece of parchment. It should be 1/8 inch thick. If any pieces crumble when rolling, just patch it back together.
Place the filling in the center of the rolled galette dough and gently bring up the edges of the dough up and over the filling.
Brush the dough with egg and place it in the oven for about 35 -40 minutes or until golden and brown.
While the galette bakes, make the whipped skyr. In a small bowl, whisk the skyr, lemon juice, black pepper and salt.
Let the galette cool slightly. Slice and serve with a dollop of the lemon skyr whip and freshly chopped herbs and enjoy!