Preheat the oven to 350 (175C) degrees with the rack in the center of the oven. Line 2 baking sheets with parchment paper.
Whisk the flour, salt and baking powder together in a medium bowl.
In a stand mixer fitted with the paddle attachment, beat the butter for 1 minute at low speed. Raise the speed to medium-high and add the sugar. Beat until light, fluffy and lighter in color, 3-4 minutes.
Beat in the eggs one at a time, then add the vanilla. Add half the creme fraiche and half the flour mixture. Stir on low speed until just mixed before adding the remaining creme fraiche and flour.
Scoop 2 tablespoon-sized portions of dough onto the baking sheets, spaced 2 inches apart (8 or 9 per sheet).
Bake one sheet at a time for 18 minutes, or until the edges begin to turn golden. Cool on a rack 5 minutes, then transfer the cookies to a rack to cool completely.
Mix the sugar, creme fraiche, milk and sea salt in a bowl until smooth. If the mixture is too thick, dribble in a tiny bit more milk. Scrape the vanilla bean with the back of a small knife, add to the bowl and mix it in.
Spread the glaze over the tops of the cooked cookies. Top with sprinkles, if you like.
The dough can mixed right before baking, or make one day ahead and refrigerate.
My favorite cookie scoop makes perfect 2-tablespoon portions of dough.