In the bowl of a food processor, pulse together flour, sugar, a pinch of salt, and cold butter. Add cold milk and pulse again. The dough should be pea-sized and resemble wet sand.
Shape the dough into a disk, cover with plastic wrap, and refrigerate for 30 -45 minutes.
Preheat oven to 375°F (190°C).
Remove the dough from the refrigerator and place on a sheet of parchment paper. Starting at the center of the dough, roll it out with a rolling pin into a circle.
Place the parchment paper with the dough on a baking sheet.
Add the filling to the center of the dough, leaving a 2-inch border. Gently fold the edges of the dough over the strawberries, overlapping the dough as necessary. Press gently to seal the edges.
Using a pastry brush, brush the crust of the galette edges with the egg yolk and sprinkle with sugar.
Bake for 25-30 min or when the dough is golden and crisp. Allow to cool on the baking sheet for 10 minutes before slicing.
How to Make the Strawberry Filling
Combine granulated sugar and cornstarch first. Add mixture to sliced strawberries, gently mix, and set aside.
Notes
Measure all ingredients correctly using a digital kitchen scale.