Make the Dough: In a mixing bowl, whisk together the all-purpose flour and salt. Cut in cold unsalted butter until the mixture resembles coarse crumbs. Gradually add very cold ice water until a dough forms, shape into a rectangle, wrap, and chill for 2 hours.

Prepare the Filling: Preheat your oven to 350°F. Toast the blanched slivered almonds on a baking sheet for about 10 minutes until golden and fragrant. Once cooled, grind them finely. In a saucepan, combine ground almonds, granulated sugar, heavy cream, all-purpose flour, almond extract, and salt. Cook over medium heat until thick for about 5-7 minutes. Allow it to cool completely.

Assemble and Bake: Preheat the oven to 375°F. Roll out the chilled dough into two large rectangles (about 12x18 inches each). Spread almond filling evenly on one rectangle, then place the other on top. Transfer to a baking sheet and bake for 25-35 minutes until golden brown (internal temperature 200-210°F).

Glaze and Finish: Cool the kringle on a wire rack for 10 minutes. In a mixing bowl, whisk together sifted powdered sugar and enough milk or heavy cream to achieve a smooth glaze. Drizzle it over the kringle and garnish with additional slivered almonds if desired.