In a large mixing bowl, whisk together 2 cups of all-purpose flour and ½ teaspoon of salt until well combined. Cut in 1 cup of cold unsalted butter until the mixture resembles coarse crumbs. Gradually add 6-8 tablespoons of ice water, mixing until the dough comes together. Shape into a rectangle, wrap in plastic wrap, and chill for at least 2 hours or overnight.

Preheat your oven to 350°F (175°C). Spread 1 cup of blanched slivered almonds on a baking sheet and toast for 8-10 minutes until golden and fragrant. Once cooled, finely grind the toasted almonds. In a saucepan, combine ground almonds, ½ cup of granulated sugar, ¼ cup of heavy cream, 2 tablespoons of all-purpose flour, 1 teaspoon of almond extract, ½ teaspoon of vanilla extract, and a pinch of salt. Cook for 5-7 minutes until thickened; let cool completely.

Once the dough has chilled, preheat your oven to 375°F (190°C). On a floured surface, roll out the dough into a 12x18-inch rectangle. Spread half of the cooled almond filling over the surface, leaving a ½-inch border. Roll up jelly-roll style, pinching seams to seal; shape into a horseshoe and transfer to a parchment-lined baking sheet.

Bake the kringle for 25-35 minutes, or until golden brown and the internal temperature reaches 200-210°F (93-99°C). Let cool on the baking sheet for 10-15 minutes before transferring to a wire rack.

Whisk together 1 cup of sifted powdered sugar, 2-3 tablespoons of milk or heavy cream, and optional almond extract until smooth. Drizzle the glaze over the cooled kringle and sprinkle with additional slivered almonds. Allow to set for 15-20 minutes before slicing and serving.