In a large mixing bowl, whisk together 2 cups of all-purpose flour and 1/4 teaspoon of salt. Cut in 1 cup of cold unsalted butter until the mixture resembles coarse crumbs. Gradually add 1/4 cup of ice-cold water, mixing until the dough just comes together. Shape the dough into a rectangle, wrap it in plastic wrap, and refrigerate for at least 2 hours to ensure optimal flakiness.

Preheat your oven to 350°F and spread 1 cup of slivered almonds on a baking sheet. Toast the almonds for about 8-10 minutes, stirring occasionally until they're golden brown and fragrant. Allow them to cool, then finely grind the toasted almonds in a food processor. In a saucepan over medium heat, combine the ground almonds with other filling ingredients, stirring until the mixture thickens and begins to simmer. Let cool completely.

Once the dough is chilled, preheat your oven to 375°F and line a baking sheet with parchment paper. Divide the dough in half, rolling each piece into a 12x18-inch rectangle on a floured surface. Spread an even layer of the almond filling along the center, leaving a 1-inch border on each side. Gently roll up the dough jelly-roll style to form a horseshoe shape, sealing the edges well.

Place the assembled almond kringle onto the prepared baking sheet and bake for 25-35 minutes until golden brown and the internal temperature registers between 200-210°F. Allow the kringle to cool on the baking sheet for 10-15 minutes before transferring it to a wire rack to cool completely.

In a mixing bowl, whisk together 1 cup of powdered sugar, 2 tablespoons of milk, and 1/2 teaspoon of almond extract until smooth. Drizzle the glaze generously over the cooled kringle and garnish with additional slivered almonds for a lovely finish. Allow the glaze to set for about 15-20 minutes before slicing and serving your ultimate homemade almond kringle.