Combine flour and salt in a medium bowl. Take butter out of the refrigerator, and grate into the flour bowl. Then using a fork, toss the butter with flour.
Measure 1/4 cup of cold water, and add a couple of ice cubes. Gradually add the ice water a little at a time, stirring the dough around the bowl with a fork. I tend to use my hands to bring the dough together but a fork works too.
NOTE: There are two ways to add the thyme to the pastry dough. One way is to add it to the dough as you are mixing it together. Another way is scattering the leaves on the counter and over the dough as you are rolling out the pastry dough.
As soon as it is moist enough to gather the dough together, form the dough into a disc and wrap in plastic wrap and place in a zip lock bag and refrigerate for about 20-30 minutes or overnight. Handle the dough as little as possible, as over mixing will cause the dough to become tough.
In a medium skillet, on medium-high heat, fry bacon until crispy. Transfer to a plate lined with paper towel. Then add and sauté leeks to the skillet for about 6-7 minutes until tender and slightly golden, add olive oil if needed, then add garlic for the last minute to allow the aroma to release. Remove from stove and set aside.
If you don't have herb goat cheese, simply use goat cheese and combine about 1/4 teaspoon of dry oregano and thyme to the goat cheese.
Preheat oven to 400°F. Line a baking sheet with parchment paper. On a lightly floured surface, roll out the disc to a 12 inch circle. Scatter the leaves from the fresh (or dry) thyme over the dough and the counter, and lightly roll over it with the rolling pin to ensure the thyme is embedded into the dough. Then transfer to the lined baking sheet.
Using a slicer or a sharp knife, thinly slice the potatoes, and transfer to a bowl. Drizzle with olive oil, and add chopped rosemary, salt and pepper.
Spread the herb goat cheese over the pastry, leaving about 1-2 inches from the edges. Then add leeks, and garlic. The arrange the potatoes over the leeks, (I left a few leeks to scatter over the potatoes) then add the bacon. Fold the edges inward toward the centers, creating a pleated design. Then brush with egg wash and bake for about 40 minutes until the crust is golden and the potatoes and bacon are crispy.
Remove galette from the oven, and allow it to cool for about 5-10 minutes. Garnish with fresh rosemary and thyme leaves.