Make the Dough:

1. Heat the Milk: In a small saucepan over medium-low heat, warm the milk until bubbles form around the edge. Remove from heat.
2. Add Butter and Almond Extract: Stir in the butter and almond extract until the butter melts completely. Let it cool while you prepare the dry ingredients.
3. Mix Dry Ingredients: In a stand mixer with a dough hook, combine 2 1/2 cups flour, yeast, sugar, and salt.
4. Combine Wet and Dry Ingredients: Add the egg and the milk mixture to the dry ingredients. Mix well, scraping down the bowl as needed.
5. Add Remaining Flour: Gradually add the remaining 1 cup of flour, 1/2 cup at a time, mixing well after each addition. Beat for 5 minutes on medium speed.
6. Knead and Rise: Place the dough on a floured surface, knead it into a ball, and then transfer it to a large bowl. Cover with plastic wrap or a damp cloth and let it rise in a warm place for 40 minutes.

Prepare the Filling:

1. Mix Filling: In a small bowl, mix brown sugar, cinnamon, and butter until combined.

Assemble the Rolls:

1. Prepare Baking Tray: Lightly grease a 9×13-inch baking tray.
2. Roll Out Dough: Roll the dough into a 16×10-inch rectangle on a floured surface.
3. Spread Filling: Spread the filling evenly over the dough, leaving a 2-inch border.
4. Roll and Cut: Roll up the dough tightly and pinch the seams to seal. Cut into 12 equal pieces using unflavored floss or a knife.
5. Arrange Rolls: Place the rolls, cut side up, in the prepared baking tray. Cover and let rise for another 30 minutes.
6. Preheat Oven: Preheat your oven to 375°F.

Bake the Rolls:

1. Bake: Bake in the preheated oven for 20 minutes or until lightly browned.

Finish and Serve:

1. Make the Icing: In a small bowl, whisk together powdered sugar, almond extract, and milk until smooth. Drizzle over the warm rolls.
2. Add Almonds: Sprinkle with toasted slivered almonds.
3. Enjoy: Serve warm and enjoy your homemade almond croissant cinnamon rolls!