Day 4 - fFavorite fFood

In a title, proper nouns, adjectives, verbs, and adverbs should have the first letter capitalised.

ThenAlso because it tastes amazing.

"then" is a really good transition word, however I think it's more appropriate when discussing the passage of events, (for example, "First I rode my bike home, then I washed my hands in my bathroom sink") When you make two statements that have no specific sequential order, I think a different transition would be better ("also", "and" "in addition").

Prepare your chicken, cut, and cook it.

This sentence is correct and concise, but I added an "Oxford comma" also known as a "serial comma". This is grammatically optional, you don't necessarily have to use this comma, but adding it in this context could clarify that cutting and cooking are two separate steps in your process, though the majority of readers would understand just fine without it.

Day 4 - fFavorite fFood

1 - Certain words in titles start with capital letters. These words include all nouns, adjectives, verbs and adverbs, as well as the first and last word in the title

2 - "Favorite," is the American spelling. Pretty much everyone else spells it "favourite." Neither is wrong, but you do need to be consistent. Your next sentence has a different spelling

My favourite / favorite food is Japanese chicken curry.

-or- for American English
-our- for anything else

FI like it first of all because it's so easy to cook.

This is called a dependant clause. If your sentence has one clause, and that clause starts with a conjunction, then it's usually wrong

ThenI also like it because it tastes amazing.

Then, cook the onions until golden and let it all simmer with somein water.

Prepare your chicken, then cut and cook it.

Add it to the stew with one or two curry-roux and let it simmer again.some more

Day 4 - fFavorite fFood

All words in the title are usually capitalized in English.

It's usually a meal I (would) prepare after a long day at work, when I am *feeling* tired or sad.

Your sentence is correct as it it. I put (would) in brackets because it's better without it. And I added *feeling* - the sentence still works without, but sounds a bit off.

Prepare your chicken,: cut and cook it.

It feeltastes so comfy and warm, perfect for cold weather!

Food can't "feel", so it should be either "it tastes so comfy..." as I put above, or "It makes me feel so comfy..."

It's usually a meal I would prepare after a long day at work, when I am tired or sad.

Feels more natural without the comma.

Then because it tastes amazing.

You can consider combining with the previous sentence, something like:
“First of all because it’s so easy to cook, second (of all) because it tastes amazing.”
“First of all because it’s so easy to cook, and because it tastes amazing.”

Prepare your chicken, cut and cook it.

It sound fine but you can consider adding a connective like:
“Next, prepare your chicken, cut and cook it.”

It makes me feels so comfy and warm, which is perfect for cold weather!

It feels more natural to express that the curry makes you feel comfy and warm (while eating it, or after you have eaten it), rather than the curry itself being comfy and warm.