In a large bowl using an electric mixer on low speed, cream the softened butter and packed brown sugar together until just combined, about 30 seconds. You don't want to incorporate too much air.
Add the egg yolk and mix on low until it's incorporated. Scrape down the sides of the bowl, then add the semolina flour, all-purpose flour, and fine sea salt.
Mix on low until the dough just barely comes together into a crumbly mixture.
Turn the dough out onto a clean work surface and gently knead it a few times to bring it together.
Shape the dough into a log about 1 to 1. 5 inches in diameter. The shape is up to you—round, square, or even triangular!
Wrap the log tightly in plastic wrap.
Chill the dough log in the refrigerator for at least 30 minutes, or in the freezer for 15-20 minutes, until firm. This step is crucial for clean slices.
Preheat your oven to 325°F / 165°C.
Line a baking sheet with parchment paper.
Unwrap the chilled dough and use a sharp knife to slice it into 1/4-inch thick rounds.
Arrange the slices on your prepared baking sheet, about an inch apart.
Sprinkle each cookie with a pinch of coarse sea salt. This is the magic touch!
Bake for 15 to 20 minutes, or until the cookies are firm and the edges are just beginning to turn a very light golden brown. They should not brown significantly.
Let the cookies cool on the baking sheet for 2-3 minutes before carefully transferring them to a wire rack to cool completely. They will be fragile while warm. Store in an airtight container for up to 3 days.
Recipe Variations
Pine Nut Cookies: For a sweeter, nuttier version, substitute granulated sugar for the brown sugar and use 1 whole egg instead of just the yolk. Omit the final sea salt sprinkle.
Fold in 1 cup (240 ml) of toasted pine nuts along with the flours.
Ginger Spice Cookies: Create a tender ginger snap by using all all-purpose flour (1 1/2 cups / 480 ml total) instead of the semolina.
Add 2 teaspoons (10 ml / 0.3 fl oz) of freshly grated ginger and 1/2 teaspoon (10 ml / 0.3 fl oz) each of ground cinnamon, allspice, and cloves along with the flour.
Black Pepper Cookies: For a peppery kick, substitute granulated sugar for the brown sugar.
Add 1/2 teaspoon (10 ml / 0.3 fl oz) of coarsely ground black pepper with the flour. Instead of sea salt, finish each cookie with an extra grind of black pepper before baking.
Sichuan Peppercorn Cookies: For a unique, tingly spice, use granulated sugar instead of brown sugar and add 1/2 teaspoon (10 ml / 0.3 fl oz) of ground Sichuan peppercorns with the flour.
Don't be shy with the salt! A quality coarse or flaky sea salt is essential for creating that signature salty-sweet flavor profile that makes these cookies so special.
