Preheat oven to 375°F. Grease a 10x15 jelly roll pan with baking spray.
In a medium saucepan, combine ½ cup butter and water over medium-high heat. Bring to a rolling boil, then immediately remove from heat and set aside.
In a large mixing bowl, whisk together flour, sugar, baking soda, and salt.
Add beaten eggs, buttermilk, vanilla, and almond extract. Mix until just combined.
Slowly pour in the boiling butter mixture while stirring constantly. The batter will be thin and runny.
Pour batter into prepared pan and spread evenly. Bake for 18-22 minutes until top springs back and toothpick comes out clean.
Cool on wire rack for 15 minutes while preparing icing.
For icing: Melt remaining ½ cup butter in heavy-bottomed saucepan over medium heat. Add brown sugar and stir constantly for 1-2 minutes until dissolved and bubbling.
Pour in milk and bring back to gentle boil, stirring frequently. Remove from heat.
Gradually whisk in powdered sugar until smooth. Add vanilla and salt.
Pour warm icing over slightly cooled cake and spread quickly to edges before it sets. Let cool completely before cutting.