Es haist mit Eier, Schinken, und Käse.

Better: Ich mache/mag es mit ....

"haben" is not completely wrong, but I would then write : Es hat Eier, .... als Belag.

Ich brate die Eier mit Butter und ich stellreiche die Butter auch auf dem Brot.

You can "stellen" the butter only if it comes fresh from the fridge and is still hard like a stone. I just imagine a slice of bread and a block of butter standing on top of it ... In practice, the butter must be at least soft enough that you can apply it like a thin covering to the bread. This is "streichen".

Yet another possibility was often applied by my late mother: She wasn't patient enough to wait until she can do "streichen", so she cut with the knife small slices of butter (perhaps 3-4 mm thickness) and placed them onto the bread. If you are doing this, it is still not "stellen", but it would be legen.

With "stellen", you have the idea of putting something in an upright position. For instance, placing a bottle of wine onto the table in the normal way would be "stellen". But if you would put it there horizontally (not recommended - don't do this at home!), it would be "legen".

Die Käse ist scharfer Cheddar.

Not wrong, but we would be more specific here. Cheddar is rarely eaten hot and spicy, so if it it, it typically contains chili. In German, you would then say "Chili-Cheddar".

Also, "ist" is not wrong, but not a good word choice either and sounds a bit childish in this context. Since you choose the cheese, it's more natural to write "Als Käse nehme ich ...".

Dier Schinken ist knusprig.

Here too, I would not use "ist", but write i.e. "Der Schinken muss knusprig sein".

However, "knusprig" does not go well with "Schinken". A "Schinken" is typically soft or sometimes hard.

The closest thing similar to "Schinken" which could be "knusprig" would be bacon, when you fry it in a pan. This would be "der Frühstücksspeck" or short "der Speck", but in this case you should say explicitly that you are frying it, because otherwise we have to guess why it is "knusprig":

Manchmal stelllege ich auch Spinat auf demas Sandwich.

Zusammen schmecken siet (all) das sehr lecker.

We don't have anything in the previous sentence where "sie" (plural) could refer to. The most recent plural word would be "Eier", but this is too many sentences back to act as a reference, and doesn't make sense with "zusammen". If you use the demonstrative pronoun "das", it is understand to refer to "all that what you have mentioned in the last or in the last few sentences", i.e. all the ingredients together taste well. Still, it is a bit unclear, because "das" could also refer to "Sandwich", and then "zusammen" would again ruin the meaning. My suggestion would therefore be to write "all das", or write it as: "Alles zusammen schmeckt sehr lecker".

BTW, since this is not a very sophisticated meal, "lecker" can be used, but be careful not to use it as a synonym for "tasty". I suggest that you get early the habit of using "sehr gut", if you want to express that something is tasty, and i.e. "ausgezeichnet" or "hervorragend", if you want to express that something is extraordinary tasty. Doing so avoids the danger of misusing the word "lecker". A nicely written article about the deeper meaning of "lecker" and possible alternatives can be found here: https://www.meinbezirk.at/leopoldstadt/c-freizeit/lecker-sagt-man-nicht_a3638745

Es hat zum Beispiel Eier, Schinken, und Käse.

Ich brate die Eier mit Butter und ich stellreiche die Butter auch auf demas Brot.

Dier Käse ist scharfer Cheddar.

Dier Schinken ist knusprig.

Manchmal stellgebe ich auch Spinat auf demas Sandwich.

Zusammen schmecken sie sehr lecker.