Preheat the oven to 400 degrees. Line a rimmed baking sheet with parchment paper.
Bring the water, butter and salt to a boil in a medium saucepan.
Add flour all at once. Mix with a wooden spoon until it forms a ball and the flour is mixed in thoroughly.
Cool for about 5 minutes or mix with a paddle attachment in a standing mixer or with a hand mixer until steam is no longer rising.
Add eggs one at a time.
Transfer the batter to a large ziptop bag or a pastry bag and pipe 2-3 inch long strips, about 1 cm thick onto the prepared baking sheet.
Bake for 15-20 minutes in the preheated oven.
Combine the sour cream, condensed milk, powdered sugar and vanilla in a standing mixer using the whisk attachment.
Add the heavy cream and continue whisking until frosting thickens.
Chill the bowl and the whisk attachment to help the frosting whip up better. I usually place the bowl and whisk attachment in the freezer for about 10 minutes. Also, use very cold sour cream and heavy cream. The frosting will not be as thick as butter cream, but it will certainly thicken as you mix it.
In a 9 inch spring form pan, spread some frosting, about 1/4 of a cup, on the bottom of the pan.
Dip the lady fingers in the frosting. Starting at the rim, arrange the lady fingers in a circle in multiple layers to fill the pan all the way to the top.
Make sure to arrange the day fingers tightly, with no spaces in between them. If you have little gaps, break the lady fingers into the size that you need.
Reserve the left over frosting in a small bowl.
Refrigerate the cake for at least a few hours. I usually keep it refrigerated overnight. It’s very important to give the cake time to set and chill, otherwise it will fall apart when you take it out of the springform pan.
Line the edges of a cake stand or plate with aluminum foil. (This is to facilitate easy clean up later.)
Run a knife or spatula around the edges of the cake.
Invert the cake onto the center of the platter and take it out of the spring form pan. Cover the top and sides with the reserved frosting.
In a small saucepan, whisk together all the ingredients EXCEPT the butter, while they are still cold.
Cook over medium heat until it comes to a boil, simmer for a few minutes, until sugar dissolves and the glaze thins out to a syrupy consistency.Whisk in the butter.
Make a pastry bag from parchment paper or regular printer paper, by taking the edges of the paper and bringing them together to form a thin point. It will be a triangular/cone shape.
Pour the hot glaze in, snip off a small hole in the tip of the paper and decorate the cake.
You need to work quickly, since the glaze will harden as it cools. (You can always return the hardened glaze to the saucepan and reheat it.)
Carefully remove the aluminum foil. Of course, you can decorate the cake any way you like. Use your imagination and enjoy.