Combine the sugar, salt, baking soda and flour in the base of a food processor and pulse until combined, about 5-6 times. Add the butter and shortening and pulse until the mixture is uniformly crumbly and sandy, about 25 times. Alternatively, you can sift together the sugar, salt, baking soda and flour into a large bowl, then use a pastry cutter to cut in butter and shortening until the mixture is uniformly crumbly and sandy.

Pour the flour/butter mixture into a large bowl. Stir in the eggs, sour cream and vanilla until the cookie dough comes together. Use your hands to form the dough into a disk. Wrap the dough in plastic wrap and place in the fridge for at least 1 hour up to 24 hours.

Preheat the oven to 400ºF with a rack in the center position. Line a baking sheet with parchment paper or a Silpat.

Using a lightly floured rolling pin on a lightly floured surface, roll the dough to ¼ -inch thickness. Using cookie cutters, cut and place on a baking sheet.

Bake the cookies until the edges are lightly browned, about 6-8 minutes. Transfer the cookies to a wire cooling rack.

Meanwhile, make the glaze. In a small bowl, mix the powdered sugar, heavy cream and salt until smooth. When the cookies have cooled completely, frost and decorate with sprinkles. Cookies will keep in an airtight container for up to a week.