1. In a mixing bowl, combine the flour, powdered sugar, and salt for the crust. Cut in the cold butter until the mixture looks crumbly. Add the egg yolk and cold water, then mix just until a dough forms.

2. Shape the dough into a disk, wrap it, and chill for 30 minutes.

3. Preheat the oven to 350°F. Roll out the dough and cut circles to fit 6 tartlet pans. Press the dough into the pans and trim the edges. Chill again for 10 minutes.

4. In a small saucepan, melt the butter for the filling over medium heat until golden brown and nutty. Remove from the heat and let it cool slightly.

5. In a bowl, whisk together the maple syrup, brown sugar, eggs, heavy cream, browned butter, vanilla extract, and salt until smooth.

6. Pour the filling evenly into the prepared tart shells.

7. Bake for 20 to 24 minutes, or until the edges are golden and the centers are just set with a slight wobble.

8. Cool the tartlets in the pans for 10 minutes, then remove and let them cool completely.

9. Finish with a light sprinkle of sea salt flakes before serving.