Whisk together all-purpose flour and salt until well combined. Cut in cold unsalted butter until it resembles coarse crumbs. Gradually drizzle in ice water, mixing until the dough holds together. Shape into a rectangle, wrap in plastic, and chill for at least 2 hours.

Preheat oven to 350°F. Toast blanched slivered almonds on a baking sheet for about 10 minutes. Once cooled, grind finely in a food processor. In a saucepan, combine ground almonds, granulated sugar, heavy cream, all-purpose flour, almond extract, and salt. Cook over medium heat, stirring until thickened (5-7 minutes). Allow to cool.

Preheat oven to 375°F. Roll out chilled dough into two rectangles (12x18 inches). Spread half of the almond filling over one rectangle, fold the second over and seal the edges. Shape into a horseshoe and bake for 25-35 minutes until golden brown.

Let the kringle cool for about 10 minutes. Whisk together sifted powdered sugar and enough milk or heavy cream for drizzling consistency. Drizzle over kringle and sprinkle remaining slivered almonds on top.