Preheat your oven to 350°F. Lightly spray a 9"x12"x3" cake pan (or baking dish) with baking spray, or butter and flour, to prevent sticking. Set aside.
In a large mixing bowl, combine the nectarines, brown sugar, lemon juice, and a pinch of salt. Toss to coat the fruit well, then set aside.
In a separate bowl whisk together the eggs, melted butter, and 2 tsp of the almond extract together until very smooth. Add the sour cream to the bowl and whisk to incorporate it into the other ingredients.
In a separate, larger bowl, stir together the flour, sugar, baking soda and powder, and the salt.
Add the wet ingredients to the dry mix. Stir this mixture together just until no pockets of flour are visible. Mixing the least amount possible ensures you won't end up with a tough cake.
Pour the cake batter into your baking dish. Use a rubber spatula to spread it out into an even layer. Arrange the slices of nectarines on top of the cake batter, pour any juice over the nectarines in the dish. Top the nectarines with the almonds. Place the pan into the oven and bake for 55 minutes to 1 hour, or until a knife (or toothpick) inserted into the very center comes out clean.
While your cake is baking, whisk together the powdered sugar, milk, and the remaining almond extract until smooth.
Once the cake has finished baking, remove it from the oven and allow it to cool for 5-10 minutes. After it has cooled, drizzle the almond glaze over the top. If you prefer a less sweet cake, just pour a little of the glaze (or omit it completely).
To serve, simply spoon a heaping portion onto plates and enjoy!