Galette Dough

1. Mix together the flour, sugar and salt in a large bowl.
2. Grate the cold butter or cut into small cubes and add to the bowl.
3. Begin working the butter into the flour with a pastry cutter or a pair of forks, but do not incorporate entirely. The dough should resemble coarse crumbs and still have flecks of butter in it.
4. Add half of the water and the apple cider vinegar. Begin mixing the dough. Gradually add the rest of the water as necessary until the dough begins to come together.
5. Turn out the dough onto your counter and knead a few times until it comes together. Wrap in plastic wrap and chill for an hour in the refrigerator.

Frangipane

1. Beat all ingredients together until soft and creamy. Alternatively, combine all ingredients in a food processor and pulse until smooth.

Frangipane Rhubarb Galette

1. Roll out the dough on parchment paper into a rough circle approximately ⅛ inch (3 mm) thick.
2. Spread the frangipane onto the dough in an even layer, leaving approximately 2 inches (5 cm) around the edges.
3. Place the rhubarb on top of the frangipane in a single layer. Sprinkle 2 teaspoons of sugar over the rhubarb.
4. Fold the edges of the dough over the rhubarb leaving the center exposed.
5. Brush the dough with a lightly beaten egg and sprinkle with almonds if desired.
6. Transfer the galette and parchment paper to a baking sheet. If using homemade dough and it seems to be quite warm, place the baking sheet in the fridge for 30 minutes before baking.
7. Preheat oven to 400°F (200°C).
8. Bake the galette for 35-45 minutes or until golden brown. 
9. Let cool for 10 minutes before serving.