kizi wo teppan ni hiroge, ryoumen ni hi wo toosita.

生地（きじ） in cooking means the uncooked mixture you are working with, so depending on the dish it can be dough, batter, or a similar mixture.

In a sentence like this, English might translate it differently depending on context:

• for pancakes or crepes: batter
• for okonomiyaki or similar foods: mixture/batter
• for bread or pastry: dough

So 生地 is a flexible cooking word, not just one exact English word in every case.

Because 生地 is the direct object of the verb 広げる.

• 生地を広げる = to spread the batter/dough

The thing being spread is 生地, so it takes を.

Also, in the second part, the same 生地 is still understood as the thing being cooked, even though it is not repeated.

Here, に marks the place/surface onto which something is spread.

• 鉄板に広げる = spread it onto the griddle / on the iron plate

So the pattern is:

• Aを Bに 広げる
• spread A onto B

In English, we often say on or onto, but Japanese uses に here.

鉄板（てっぱん） literally means iron plate, but in cooking it often means a griddle, hot plate, or teppan-style metal cooking surface.

So depending on context, a natural English translation might be:

• griddle
• hot plate
• metal plate
• teppan

It does not always have to sound as literal as iron plate in English.

広げ、 is a written-style way of connecting actions. It is the continuative form of 広げる and functions a lot like 広げて here.

So:

• 生地を鉄板に広げ、両面に火を通した。
• 生地を鉄板に広げて、両面に火を通した。

These are very similar in meaning.

The version with 、 and the continuative form sounds a bit more:

• written
• concise
• recipe-like
• explanatory

You will often see this style in instructions, manuals, and written descriptions of procedures.

Literally, 火を通す means something like to pass heat through something.

But as a normal Japanese cooking expression, it means:

• to cook through
• to apply heat until done
• to let the inside get properly cooked

So 両面に火を通した means that both sides were cooked with heat, not just lightly touched by heat.

This expression focuses more on properly cooking something than on browning or grilling it.

Because in the expression 火を通す, the direct object is 火, so 火 takes を.

That leaves 両面 as the target/location affected by the heat, so it is marked with に:

• 両面に 火を通す
• apply heat to both sides
• cook both sides through

So the structure is:

• 両面に = to both sides
• 火を通した = applied heat / cooked through

Using 両面を火を通した would not sound natural.

They are similar, but the nuance is different.

• 両面を焼いた = grilled/fried/browned both sides
• 両面に火を通した = cooked both sides through with heat

焼く focuses more on the act of grilling/frying/roasting and the surface result.

火を通す focuses more on making sure the food is actually cooked, including the inside if relevant.

So 火を通す is often used when the speaker wants to emphasize doneness, not just surface browning.

The subject is omitted, which is very normal in Japanese.

Depending on context, it could mean:

• I spread the batter on the griddle and cooked both sides through
• She spread the batter on the griddle and cooked both sides through
• Spread the batter on the griddle and cook both sides through (recipe/instruction style)

Japanese often leaves out the subject when it is obvious from context.

On its own, the sentence is simply a past description:

• spread the batter on the griddle and cooked both sides through

But in Japanese, recipe/procedure writing can sometimes use plain forms in a descriptive way, especially when explaining what was done. So without more context, it could be either:

1. a narration of what someone did, or
2. a recipe/explanatory sentence describing the step in a matter-of-fact way

If it were a more direct instruction, you might also see forms like:

• 広げて、両面に火を通す
• 広げ、両面に火を通す

So the past tense here does not automatically mean it cannot appear in cooking instructions; context matters.