For filling and topping:
To make crust:
1. Pulse flour, sugar, and salt in a food processor to blend.
2. Add butter and pulse until mixture resembles coarse crumbs.
3. Add 2 tablespoons ice water and pulse until dough clumps together, adding more ice water by teaspoonfuls if dough is dry.
4. Gather dough into ball and flatten into disk. Wrap in plastic and chill at least 2 hours.
To make filling:
1. Combine rhubarb, 1/4 cup sugar, and cinnamon in medium bowl.
2. Let stand at least 30 minutes and up to 1 hour.
3. Meanwhile, position rack in center of oven and preheat to 350°F.
4. Remove dough from refrigerator and let soften 10 minutes at room temperature.
5. Place large sheet of parchment paper on work surface and sprinkle with flour.
6. Roll out dough on parchment to 12-inch round.
7. Transfer parchment with dough to large rimmed baking sheet.
8. Spread rhubarb on dough, leaving 1-inch border at edge.
9. Gently fold dough border over outer edge of rhubarb topping, pleating as needed.
10. Sprinkle 2 tablespoons sugar over rhubarb.
11. Dot rhubarb with butter cubes.
12. Brush edge of dough with beaten egg yolk.
13. Sprinkle border with 1 tablespoon sugar.
14. Bake until rhubarb is tender and juices bubble, about 1 hour.
15. Cool at least 30 minutes.
To make topping:
1. In a small bowl, beat together goat cheese, heavy cream, and remaining 2 tablespoons sugar until smooth and creamy.
2. Cut galette into wedges. Serve warm or at room temperature with goat cheese cream.