Part 1: Making the Dough

1. Combine Dry Ingredients: In a large bowl, whisk together the flour and salt.
2. Incorporate Cold Butter: Add the cold, cubed butter to the flour mixture. Using a pastry blender or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs, with some pea-sized pieces of butter remaining. The goal is to keep the butter pieces intact to create layers in the pastry. Work quickly to prevent the butter from warming up too much.
3. Add Ice Water: Gradually add the ice water, one tablespoon at a time, mixing gently after each addition. Mix just until the dough comes together and forms a shaggy mass. Do not overmix. It’s okay if the dough looks a bit rough at this stage.
4. Form Dough and Chill: Turn the dough out onto a lightly floured surface. Gently gather it into a rectangle, about 1 inch thick. Wrap the dough tightly in plastic wrap and refrigerate for at least 2 hours, or preferably overnight. This chilling time allows the gluten to relax and the butter to firm up, making it easier to roll out and preventing the pastry from becoming tough.

Part 2: Making the Filling

1. Toast Almonds (if not already toasted): Preheat your oven to 350°F (175°C). Spread the slivered almonds on a baking sheet in a single layer. Toast for 8-10 minutes, or until lightly golden and fragrant, stirring halfway through to prevent burning. Let them cool completely.
2. Grind Almonds: Once cooled, finely grind the toasted almonds using a food processor or a nut grinder. Be careful not to over-process into almond butter. You want a fine, crumbly texture.
3. Combine Filling Ingredients: In a medium saucepan, combine the granulated sugar, heavy cream, ground almonds, flour, almond extract, vanilla extract, and salt.
4. Cook Filling: Cook the filling over medium heat, stirring constantly, until the mixture thickens and comes to a simmer. This usually takes about 5-7 minutes. Continue to cook for another minute, stirring constantly, to ensure the flour is cooked and the filling is smooth.
5. Cool Filling: Remove the filling from the heat and let it cool completely to room temperature. As it cools, it will thicken further. Cooling the filling is crucial before assembling the Kringle, as warm filling can melt the butter in the dough and make it difficult to handle.

Part 3: Assembling and Baking the Kringle

1. Preheat Oven and Prepare Baking Sheet: Preheat your oven to 375°F (190°C). Line a large baking sheet with parchment paper.
2. Divide and Roll Dough: Remove the chilled dough from the refrigerator. Divide the dough in half. Work with one half at a time, keeping the other half refrigerated to maintain its cold temperature. On a lightly floured surface, roll out one piece of dough into a large rectangle, approximately 12×18 inches and about ¼ inch thick. Try to keep the rectangle as even in thickness as possible for even baking.
3. Spread Filling: Spread half of the cooled almond filling evenly over the rolled-out dough, leaving a ½-inch border around the edges.
4. Roll and Shape: Starting from one long side, roll up the dough jelly-roll style, enclosing the filling. Pinch the seam to seal. Gently curve the roll into a horseshoe or oval shape and place it on the prepared baking sheet. Bring the ends together and gently pinch to seal, forming a Kringle shape. You can also leave it as a straight log if preferred.
5. Repeat with Remaining Dough: Repeat steps 2-4 with the remaining dough and filling.
6. Bake: Bake for 25-35 minutes, or until the Kringle is golden brown and cooked through. The baking time may vary depending on your oven. Keep an eye on it and adjust baking time as needed.
7. Cool: Let the Kringles cool on the baking sheet for about 10-15 minutes before transferring them to a wire rack to cool completely. Cooling slightly on the baking sheet helps prevent the bottom from becoming soggy.

Part 4: Making the Glaze and Finishing

1. Prepare Glaze: While the Kringles are cooling, make the glaze. In a small bowl, whisk together the powdered sugar, milk or cream, and almond extract (if using) until smooth. Add more milk or cream, one teaspoon at a time, to reach your desired glaze consistency. It should be pourable but not too runny.
2. Glaze Kringles: Once the Kringles are completely cool, drizzle the glaze evenly over the top of each Kringle. You can use a spoon or a piping bag for a more decorative finish.
3. Garnish (Optional): If desired, garnish the glazed Kringles with slivered almonds or chopped toasted almonds while the glaze is still slightly wet, so they adhere well.
4. Set Glaze: Allow the glaze to set completely before slicing and serving. This will take about 15-20 minutes.