Prep your ice cream and dulce de leche the day before if possible.
For the ice cream layers, prep your cake pans with parchment paper and scoop vanilla ice cream into the pan. Use a spoon to flatten and create a leveled top. Place in the freezer for 1-2 hours. Remove from the pan while still in parchment and place into a large Ziploc bag and place it back in the freezer. Repeat for 2 more layers.
Start the dulce de leche sauce you will pour the can of sweetened condensed milk into a mason jar. Place the inner lid askew on top of the jar. Place the jar in a pot and fill the pot with water up to the line where the condensed milk hits. Boil the water over medium heat.
Use tongs to remove the lid every 30 minutes and with a long spoon stir the insides for 15-30 seconds. Keep boiling for about 3 hours. The boiling water may make the mason jar shake around and can be very noisy.
Occasionally add more water to the pot since it will evaporate over time. Use boiling water from a tea kettle, NOT cold water as that may cause the glass to break.
Once the milk has boiled for 3 hours, remove from heat and using tongs, take the mason jar out of the pot and place onto a plate or hot pad to dry and cool for about 2 hours. Then tighten the lid and refrigerate for at least 6 hours. Overnight is best.
To make the churro cake layers, you will need to preheat your oven to 350° F. Prep your cake pans with parchment paper. I use a bit of oil or butter on the pan to help the parchment stick.
In a sauce pan heat your butter, salt, sugar and water over medium heat and let boil. Once the butter has melted, add flour all at once and stir with a wooden spoon. Stir until incorporated and continue to stir over heat for about 30-60 seconds. It should be smooth.
Remove pot from the heat and add one egg at a time. Mix quickly and thoroughly before adding a new egg. You don't want the egg to cook in the heated mixture. This will be a bit of an arm work out.
Once all of the eggs are mixed in add your vanilla extract and mix.
Scoop your dough into the cake pan and use an offset spatula or spoon to create an even leveled top. It won't blend into the side of the pan, like a normal cake - this is a donut, don't forget. The edges might be a little oddly shaped.
Bake for 45 minutes or until the entire outside is golden brown. Remove from the oven and pull the churro layer out by the parchment and cool on a rack.
Mix the sugar and cinnamon together in a bowl.
Once completely cooled brush the entire churro layer with melted butter. Lay the churro down on a cookie sheet and pour some of the cinnamon sugar mixture on top. Make sure you coat the top, side, and bottom.
Repeat steps 10-13 for the remaining 3 churro layers.
When you are ready to assemble alternate layering churro and ice cream layers. The more frozen the ice cream the better. Pour dulce de leche sauce over the top and allow to drip. Slice up and serve!