Step 1

Make the dough: In a large bowl, mix together the flour, salt, and sugar. Add the butter and toss to coat. Using your hands, work the butter into the flour until the mixture resembles a coarse meal.

Step 2

Make a well in the center of the butter/flour mixture and pour in the buttermilk. Working quickly so the butter doesn’t soften, use your hands to form a shaggy dough.

Step 3

Turn the dough out onto a lightly floured surface and knead until it comes together, being careful not to overwork. Form the dough into a 7-inch (18 cm) square about 1 inch (2.5 cm) thick. Cut into 8 equal pieces and form into discs. Wrap the discs in plastic wrap and chill in the refrigerator for at least 1 hour, or overnight.

Step 4

Make the filling: Bring a large pot of salted water to a boil over high heat. Add the sweet potatoes, then reduce the heat to medium-high and cook for 10–12 minutes, or until the sweet potatoes are very tender. Drain, then transfer to a medium bowl and let cool for about 10 minutes.

Step 5

To the bowl with the sweet potatoes, add the melted butter, milk, brown sugar, vanilla, cinnamon, salt, and egg. Mix well with a fork, mashing the sweet potatoes, until smooth and well combined. Let cool to room temperature.

Step 6

Make the streusel: Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper or a nonstick mat.

Step 7

In a medium bowl, mix together the flour, granulated sugar, brown sugar, salt, and cinnamon. Work the butter into the dry ingredients with 2 forks until crumbly. Add the chopped pecans and mix well.

Step 8

Spread the streusel on the prepared baking sheet. Bake for 12–15 minutes, stirring halfway, until golden brown. Remove from the oven and let cool slightly, then crumble and let cool completely before using. The streusel will keep in an airtight container for up to 1 week.

Step 9

Assemble the galettes: Increase the oven temperature to 400°F (200°C). Line 2 baking sheets with parchment paper.

Step 10

Roll out each disc of pie dough into a 7-8 inch (18-20 cm)round, trimming the edges for even circles. Spoon about 3 tablespoons of the sweet potato filling into the center of each round. Fold the edges of the dough up and over the filling, leaving an opening in the center. Transfer the galettes to the prepared baking sheets, 4 per pan.

Step 11

Brush with the dough with the egg wash and sprinkle with the turbinado sugar.

Step 12

Bake the galettes for 25 minutes, then rotate the pan and bake for another 10 minutes. Remove from the oven and top each galette with about 1 tablespoon of the streusel and 1 tablespoon of marshmallows, then return to the oven and bake for another 5 minutes, or until the marshmallows are browned and bubbling.

Step 13

Serve immediately.

Step 14

Enjoy!