ryoumen ni hi wo toosu.

It is read:

りょうめん に ひ を とおす

• 両面 = りょうめん
• 火 = ひ
• 通す = とおす

So the full reading is りょうめんに ひをとおす.

両面 means both sides or both surfaces.

In a cooking context, it usually refers to the two sides of something like:

• meat
• fish
• bread
• tofu
• pancakes

So it is talking about cooking side A and side B, not just one side.

Here, に marks the target or place affected by the action.

So 両面に火を通す is basically:

• apply heat to both sides
• cook both sides

The idea is not that both sides are the direct object of 通す.
Instead, 火 is the thing being passed through/applied, and 両面に tells you where that heat is being applied.

A rough literal breakdown is:

• 両面に = to both sides
• 火を通す = pass heat through / cook with heat

Yes, it is an idiomatic expression.

Literally, 火を通す looks like pass fire through, but in natural English it means:

• to cook
• to heat through
• to cook until heat has gone through
• to cook thoroughly enough

In recipes, 火を通す often emphasizes that the food should be properly cooked, not left raw inside.

Examples of the nuance:

• chicken: make sure it is cooked through
• vegetables: heat them enough
• steak or fish: cook both sides with heat

So this expression is very common in cooking Japanese.

Because in the expression 火を通す, 火 is treated as the direct object of 通す.

Even though that may sound strange in English, Japanese often uses set expressions like this.
So you should learn 火を通す as a chunk.

It is similar to how English has fixed expressions that are not fully literal.

In this sentence:

• 火 = the heat
• を = marks it as the object
• 通す = to pass through / apply through

So grammatically, 火を通す stays together as one expression meaning cook through.

Yes, that basic idea is still there.

The core meaning of 通す is to let something pass through or to put something through.

In cooking, that idea becomes:

• let heat pass through the food
• get heat into it
• cook it through

So the original sense of 通す helps explain the expression, even though the whole phrase is best understood as the cooking idiom 火を通す.

Yes. This is very normal Japanese, especially in recipes and instructions.

Japanese often omits the subject when it is obvious from context.
In a recipe, the implied meaning is something like:

• You should cook both sides
• Cook both sides through

Recipes often use the plain form like this in a short, instruction-style way.

So although it looks incomplete from an English point of view, it is perfectly natural Japanese.

In recipes, manuals, and step-by-step instructions, Japanese often uses the plain form to give directions in a neutral, concise style.

So 両面に火を通す。 functions like an instruction:

• Cook both sides
• Heat both sides through

It is not necessarily a casual statement to a friend.
In this context, it is more like a recipe step.

This style is common in written instructions because it is short and efficient.

Good question. They overlap, but the focus is different.

• 焼く = grill / fry / bake / cook by direct heat
• 火を通す = cook through / apply heat until done

So:

• 焼く focuses more on the method
• 火を通す focuses more on the result of heating

For example, something can be 焼かれている but still not fully cooked inside.
If you say 火が通っている, it means the heat has gone through and it is properly cooked.

So in this sentence, the important point is not just brown both sides, but make sure both sides get properly cooked with heat.

Usually it suggests cook both sides properly with heat, not just briefly touch them to the pan.

However, the exact degree depends on context:

• in some recipes, it may simply mean cook both sides
• in others, it may imply until done / until no longer raw

The phrase 火を通す often carries the idea of not leaving it raw, so it can sound stronger than just lightly cook.

No, that would not be natural.

With 火を通す, the usual pattern is that the place or target takes に, as in:

• 全体に火を通す = cook the whole thing through
• 両面に火を通す = cook both sides through

If you want to use を with 両面, you would normally switch to a different verb, such as:

• 両面を焼く = grill/cook both sides
• 両面をこんがり焼く = brown both sides nicely

So for this sentence, 両面に is the natural form.

Depending on context, natural translations include:

• Cook both sides.
• Cook both sides through.
• Apply heat to both sides.
• Cook it on both sides.

If the recipe is emphasizing doneness, Cook both sides through is especially close in nuance.