Preheat the oven to 350 degrees. Spray or line 3 - 8 inch cake pans, set aside.
In a medium bowl, combine the milk, egg whites and vanilla. Whisk to combine.
In the bowl of a stand mixer, combine the flour, cornstarch, baking powder and salt. Mix to combine.
Cut the butter into thin slices and add to the dry mix. Use the paddle attachment and mix for about a minute or until the butter is about pea size pieces.
Add the mixture to the bowl and mix on low speed until combined.
Add the sugar and brown sugar. Mix well, scraping the sides often.
Use a food processor, if needed, to chop the pecans into small pieces. Add the pecans to the batter and fold to combine.
Divide the batter between the three prepared cake pans. Bake in the preheated oven for about 20-25 minutes or until the center is set and the edges are starting to brown. Allow to cool completely before decorating.
For the pecan pralines - In a medium bowl, combine the egg white, water and brown sugar. Whisk to combine.
Add in the pecans and toss to coat.
Transfer the pecans to a baking sheet lined with parchment for easy cleanup.
Toast the pecans in the preheated oven for about 15 minutes, stirring every 3-4 minutes, until the pecans are toasted and crispy. Allow to cool and then break apart.
For the frosting - in the bowl of a stand mixer, whip the butter for about a minute on medium speed.
Add in the softened cream cheese and whip for about another minute or until smooth and combined well.
Add in the powdered sugar, bourbon (if using) and salt. Mix on low speed until combined. Then bump up the speed to medium and whip until smooth. Scrape the sides often.
To assemble - place one cake layer on a display platter. Spread a thin layer of frosting over the top of the cake.
Place the next cake on top of the icing and repeat with another thin layer of frosting.
Repeat with the last cake layer and a thin layer of icing over the top and sides of the cake for a crumb coat. Chill in the fridge for about 30 minutes to set.
Remove the cake from the fridge and cover the cake in another thin layer of frosting.
Transfer the remaining frosting to a piping bag fitted with a large star tip.
Pipe small mounds around the edges of the cake.
Place a single pecan on the top of each mound.
Place a layer of pecans around the bottom of the cake as a border.
Sprinkle the remaining pecans on top of the cake in the center of the piped mounds.
Chill until ready to serve.