Step 1

Cut the cold butter into 1/4" (6mm) square pieces. Place the butter in the freezer for at least five minutes.

Step 2

Whisk the milk and apple cider vinegar together until it bubbles. It will thicken as it sets for five minutes. This is your buttermilk.

Step 3

In a large bowl, mix the flour, sugar and salt. Using your hands (or a pastry cutter), cut in the butter by pinching/flattening the butter as you toss it with the flour. The butter should remain in larger chunks, such as almond size. Work quickly to keep the butter cold.

Step 4

Pour in the milk mixture. Use your hands to incorporate the buttermilk, folding and pressing the mixture. Flattening out the butter is okay. To test hydration, grab a hand full of dough and squeeze it. If it holds together, it's ready for further shaping without adding more liquid. If it's still crumbly or falls apart, add a splash of milk or cold water and continue folding and pressing to a shaggy consistency. If the butter is starting to get a bit warm at this point, put the mixture in the freezer for about 5 minutes. We want the dough to stay as cold as possible.

Step 5

On a lightly floured work surface, dump out the shaggy dough. Using a bench scraper, fold and press the dough at least 6-8 times, eventually shaping the mixture into a rough rectangle. Use the heel of your hand to press and schmear the dough onto the work surface. Gather the dough once again using the bench scraper and shape into a rectangle. Fold and press the dough over and on top of its self 7-8 more times. This helps to hydrate the dough and build flaky layers.

Step 6

Gather all the bits together and shape into a rough disk approximately 1/2" (12mm) thick. Double wrap in parchment paper and rest in refrigerator for at least two hours. If you can, make one day ahead as this renders the dough easier to work with. MAKE AHEAD TIP: at this point the dough may be rested in the fridge for up to two days or frozen for up to two weeks. Wrap snugly in parchment, then refrigerate or freeze in a lidded container or freezer bag.

Step 7

Remove the dough from the refrigerator and allow it to rest at room temperature for at least an hour. This allows it to soften as to make it more pliable to roll out.

Step 8

While the dough is resting, in a small mixing bowl, mix the sugar, salt and corn starch. Set aside. In a large mixing bowl, add the blueberries, sugar mixture, lemon zest and juice and vanilla. Toss to coat the blueberries (you can use a spatula here, but be gentle as to not squash the blueberries ). Set aside.

Step 9

Dust the top of the pastry with flour and dust your rolling pin. Roll the dough to 1/8" (3mm) thick to about 13 - 14 inches round, flouring the work surface and rolling pin as needed to prevent sticking. Transfer the dough to a parchment lined sheet pan.Mound the blueberry mixture evenly in the center of the pastry leaving about 2 inch (5cm) boarder. Fold edges over the blueberries, overlapping and pleating the edges all the way around 7-8 times, leaving the center open.

Step 10

Freeze the galette for at least 20 minutes while the oven preheats to 375F (190C). MAKE AHEAD TIP: The assembled galette can be frozen solid at this point. Simply allow it to freeze then wrap snugly in parchment and foil. Freeze for up to two weeks. When ready to bake, bake on a parchment lined sheet pan as indicated below.

Step 11

Arrange a baking rack in the center of the oven and preheat the oven to 375F (190C).

Step 12

Just before baking, whisk the egg with 1 Tbs water and egg wash the crust. Alternatively, use milk or nut milk here (with no additional water) for egg free. Optionally sprinkle the pastry with turbinado or raw sugar to finish the crust.

Step 13

Bake the galette for 45-50 minutes until the center is bubbly and the pastry is golden (same for a frozen galette). Rest the galette at room temperature for at least 20 minutes before slicing. Serve with vanilla bean ice cream.

Step 14

The baked galette can be stored at room temperature for up to two days. For longer storage, wrap snugly in parchment and foil, then into a freezer bag for a few weeks. Reheat at 350F for about 15 minutes