Preheat oven to 350 degrees and grease a large cookie sheet (around 13x18'' or 15x11).
In a medium bowl, mix together the flour, sugar, baking soda and salt.
In another small bowl, mix together the sour cream, eggs and almond extract.
Add sour cream and egg mixture to the flour mixture and stir together just until combined.
Add water and butter to a medium saucepan over medium heat. Bring mixture to a boil.
Once the mixture is boiling, remove from heat and add to the batter, mixing to combine.
Pour batter into prepared pan and smooth with a spatula into an even layer.
Bake in preheated oven for 17-20 minutes or until a toothpick inserted comes out clean.
When the cake is about 5 minutes away from being done cooking, prepare the frosting.
For the frosting:
Add cream and butter to a saucepan. Bring mixture to a boil.
Once boiling, remove from heat and stir in powdered sugar and almond extract. Whisk mixture together with a whisk or hand mixer to get rid of any lumps.
Pour warm icing over warm cake. Use a spatula to gently spread it evenly over the cake.
Top with toasted slivered almonds. Allow cake to cool before serving.