• If you use an air fryer, you want to halve the recipe and use a 5 or 6-inch round pan
• If you bake with oven, you can use 9-inch bundt cake pan that is at least 3 inches tall, 8-inch tube pan (1 piece,don't use a loose bottom pan because the batter is thin and it will leak out ), 8 x 3 inches round pan, or 7 x 3 inches square pan
• For conventional oven, preheat oven to 400 F (200 C). For convection oven (top and bottom heat), use bottom heat only or if you can't adjust, lower the temperature by 20 F (15 C). Preheat with an empty baking sheet placed at the lowest rack in your oven, for at least 15 minutes. You want to make sure that your oven is really hot to make sure the cake batter won't separate during baking
• For air fryer: preheat at 375 F (190 C) for 5 minutes
• Grease the bottom of the pan. Line the pan with parchment paper at the bottom for easier release. If you use a bundt or tube pan, grease and flour the pan. Tap out excess flour

Caramelize the sugar:

• Put the sugar on a saucepan over low-medium heat. The sugar will slowly melt. Swirl the pan around as it helps to speed up the caramelization and to prevent the sugar from getting burn. Control the heat. If the sugar burns, the cake will taste bitter. Don't stir as the sugar will crystalize
• Once the sugar has turned golden brown, slowly pour in the hot water. It will bubble vigorously. Be careful, this is hot sugar. The sugar will crystalize a bit but don't worry, keep stirring over medium heat until dissolved and then add butter and stir until butter almost melt. Remove from the heat and keep stirring until all butter melts completely. Let the mixture cool down before adding to the batter

Prepare the batter:

• Whisk the dry ingredients and set aside
• Use a hand whisk to beat the eggs, condensed milk, and vanilla extract until a bit foamy. Add 1/3 of the flour mixture alternating with the caramel sugar. Strain the batter to get rid of any lumps
• In the video, I suggested to rest the batter for at least 30 minutes. This is no longer necessary as I didn't see any difference in terms of honeycomb texture

Baking in an air fryer:

• Remove the inner basket of an air fryer. Place a metal trivet inside the air fryer box. Pour the cake batter into the prepared pan. The pan should be only about 3/4 full. Don't fill up all the way or the cake will overflow. Set the pan on top of the trivet and lower temperature to 340 F (170 C) and bake for 20 minutes and then lower the temperature to 300 F (150 C) and bake for another 10 minutes. The top may get burnt a little bit, but this is pretty common with air fryer. Use a skewer and insert into the center of the cake. It should come out dry. If it comes out still wet, bake in 3-5 minute increment until a cake tester inserted comes out clean.

Baking in the oven:

• Place the cake pan on the preheated empty pan at the lowest rack in the oven and lower the temperature to 375 F (190 C) and bake for 40 minutes and then move to the middle rack and bake for another 8-10 minutes or until a toothpick inserted into the cake comes out clean. Because every oven is different, you need to adjust the temperature and timing as you see fit

Cool down the cake:

• Wait for 20 minutes and then remove the cake from the pan to let it cool down completely before slicing the cake

Serving:

• I notice that the one made with butter will harden when room temperature is colder (which makes sense because it's almost winter where I am) and the one made with oil, stays soft (which makes sense too). My point is, the one made with butter is much more aromatic, but if it's cold where you are, you may find the cake is harder, but not because the cake has dried out, but it needs to be reheated in the microwave briefly to soften the butter and it tastes really good!!! (just thought I would share)

How to store:

• They can be kept at room temperature in an air-tight container for 3-4 days. I don't recommend storing in the fridge because it dries out the cake. However, they freeze well. Wrap them in plastic wrap and then put in a freezer-friendly bag. They can be kept frozen for up to one month for the best quality. When ready to serve, thaw at room temperature and heat up in a microwave for a few seconds to soften (because it has butter and butter solidifies when it's cold). The cake is back to its soft and moist state again