komugiko wo mizu de toku tuide ni, butabara mo kizande.

Because 小麦粉 is the thing being acted on.

In A を B で 溶く:

• A = the thing you dissolve or loosen up
• B = the material/tool you use to do it

So here:

• 小麦粉を = the flour is the direct object
• 水で = water is what you use

This is why it is not 小麦粉で. That would suggest the flour is the means/tool, which is not the intended meaning.

Here で marks the means or material used to perform the action.

So 水で溶く means something like:

• dissolve it with water
• loosen it up using water

By contrast:

• 水に often marks a destination, result, or something like into water / in water
• 水と means with water in the sense of together with, but not usually the tool/material nuance needed here

In this sentence, で is the natural choice because water is functioning as the substance used to make the flour dissolve or mix smoothly.

Not exactly.

溶く（とく） often means:

• to dissolve
• to dilute
• to beat into liquid
• to loosen something up in a liquid

In cooking, it is commonly used for things like:

• 小麦粉を水で溶く = dissolve/mix flour with water into a smooth liquid or paste
• 卵を溶く = beat eggs

So it overlaps with mix, but it is more specific than a general mix. It suggests making something blend into liquid or become smooth.

A more general verb would be 混ぜる, but 溶く fits better when the idea is that the flour is being worked into the water.

ついでに means:

• while you're at it
• on the occasion of doing that
• as a side thing while doing the main thing

So 小麦粉を水で溶くついでに means:

• while you're mixing the flour with water
• since you're doing that anyway

Then the speaker adds another task:

• 豚バラも刻んで = chop the pork belly too

So the whole flow is: While you're doing the flour-and-water part, go ahead and chop the pork belly too.

Because verb dictionary form + ついでに is a common pattern.

It means:

• while doing X
• taking the opportunity of doing X
• while you're at X

Examples:

• 買い物に行くついでに、郵便局にも寄る
  While I'm going shopping, I'll stop by the post office too.
• 掃除するついでに、古い紙も捨てた
  While cleaning, I threw away old papers too.

So here:

• 溶くついでに = while doing the dissolving/mixing

This is a fixed, natural grammar pattern.

も means also / too.

It shows that chopping the pork belly is an additional action, not the main one.

So the sentence has this structure:

• First task: 小麦粉を水で溶く
• Additional task: 豚バラも刻んで

The nuance is:

• mix the flour with water, and also chop the pork belly
• while you're at it, chop the pork belly too

Without も, it would sound more like just another plain instruction. With も, it clearly connects the second task as an extra thing to do.

You would never say もを together like that.

When も replaces を, が, or sometimes other particles, the original particle is usually dropped.

So:

• 豚バラを刻んで = chop the pork belly
• 豚バラも刻んで = chop the pork belly too

Here も is doing the job of highlighting 豚バラ as an additional item, so を is not used.

This is very common:

• 水を飲む → 水も飲む
• 野菜を切る → 野菜も切る

Because this is a casual, shortened instruction style, very common in spoken Japanese and especially natural in cooking contexts.

～て at the end can sound like:

• please do this
• do this, and...
• go ahead and do this

So 刻んで here is an informal directive, softer than a blunt command like 刻め, and shorter than 刻んでください.

In recipes, conversations, and kitchen instructions, this kind of ending is very natural.

You can think of it as an omitted ください or simply a conversational instruction.

Yes, there is a difference.

• 切る = to cut (general word)
• 刻む = to chop finely / mince / cut into small pieces

So 豚バラも刻んで suggests chopping the pork belly into smaller pieces, not just making one cut.

In cooking, 刻む is often used when ingredients need to be prepared in a more detailed way.

Yes. 豚バラ usually refers to 豚バラ肉, meaning pork belly.

In cooking Japanese, ingredients are often named in shortened forms if the meaning is obvious.

So:

• 豚 = pig/pork
• バラ = belly/flank cut
• 豚バラ = pork belly

This shortened style is very common in recipes and everyday kitchen talk.

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

From context, the implied subject is usually:

• you, if someone is giving instructions
• or sometimes we, depending on the situation

Because this sentence sounds like a cooking instruction, the natural interpretation is:

• You mix the flour with water, and while you're at it, chop the pork belly too.

Japanese often leaves out subjects when they are obvious from context.

No. Normal Japanese would usually be written without spaces:

小麦粉を水で溶くついでに、豚バラも刻んで。

Spaces are often added only for learners, subtitles, or teaching materials to make the sentence easier to read.

So the spaces here are just a study aid, not standard Japanese writing.