Add the eggs, kefir, milk, melted butter, flour, sugar and salt to a blender and pulse twice for 15 seconds each.
Place the covered blender in the refrigerator for 45-60 minutes.Slice the apples and make the whipped cream and caramel sauce while the crepe batter chills.
Lightly grease an 8 inch nonstick skillet with butter and heat on medium-low. Add about ¼ cup of batter to the pan and tilt it around so that the bottom is completely covered. Let it cook for 45-60 seconds, then flip it and cook the other side for another 45-60 seconds. Carefully transfer the crepe to a plate and repeat until you're out of batter.
Caramel Sauce
In a small/medium saucepan, combine the light brown sugar, butter and salt. Stir constantly over medium-low heat until it starts to simmer. Let it simmer for 1-2 minutes.
While stirring, add the cream and bring it back to a simmer. Let it simmer without stirring for 2-3 minutes. Remove from heat and let it cool while whisking every 5-10 minutes.
Whipped Cream
Pour the cream into a large bowl and whisk with a hand mixer from low to medium speed until it starts to thicken. Add the vanilla extract and powdered sugar (a little bit at a time so it doesn't fly everywhere) and continue mixing from medium to high speed until it reaches stiff peaks.Refrigerate until you're ready to assemble the cake.
Assemble the Crepe Cake
Spread whipped cream on top of a crepe, then add the thinly sliced apples and caramel sauce. Stack a crepe on top and repeat until all crepes are used.
Notes
Store leftovers in the refrigerator for 2-3 days.The provided nutrition information is an estimate for the entire cake, the calorie accuracy is not guaranteed.