Какой бы десерт ты ни выбрала, я всё равно попрошу хотя бы одну слойку и один кусочек рулета.

This is a very common Russian pattern meaning whatever dessert you choose or no matter which dessert you choose.

The pattern is:

• question word
  • бы
    • ... + ни
      • verb

So here:

• какой = what kind of / which
• бы
• ты
• ни
• выбрала

Together, it creates a concessive meaning: the result in the main clause stays true regardless of the choice.

A very literal unpacking would be something like:

• Which dessert you might choose, I’ll still ask for...

But in natural English, it is simply Whatever dessert you choose...

Because after бы, Russian normally uses the past-form of the verb to build a subjunctive/conditional-style meaning.

So выбрала here does not mean actual past time. It is part of the construction.

Compare:

• ты выбрала = you chose or you have chosen
• ты бы выбрала = you would choose
• какой бы десерт ты ни выбрала = whatever dessert you choose / would choose

So the form looks past, but in this structure it is really expressing a hypothetical or unrestricted choice, not a completed past action.

Because the verb agrees with the person being addressed.

• выбрала = feminine singular
• выбрал = masculine singular
• выбрали = plural, or polite you

So this sentence is addressed to one woman or one girl.

If you were speaking to a man, it would be:

• Какой бы десерт ты ни выбрал...

If you were speaking politely or to more than one person:

• Какой бы десерт вы ни выбрали...

Because ни is part of this fixed concessive pattern.

In this sentence, ни does not mean simple negation. It helps create the meaning no matter which / whatever.

So:

• Какой бы десерт ты ни выбрала... = whatever dessert you choose...

But with не, the meaning would change completely:

• ты не выбрала = you did not choose

That would be ordinary negation, which is not what is happening here.

Because какой agrees with десерт, and here десерт is the direct object of выбрала.

Десерт is:

• masculine
• singular
• inanimate

For masculine inanimate nouns, the accusative form looks the same as the nominative form. So:

• nominative: какой десерт
• accusative: какой десерт

That is why you see какой, not какого.

If the noun were feminine, you would see a different form:

• Какую булочку ты ни выбрала...

Because Какой бы десерт ты ни выбрала is a subordinate clause, and it is separated from the main clause by a comma.

Structure:

• subordinate clause: Какой бы десерт ты ни выбрала
• main clause: я всё равно попрошу хотя бы одну слойку и один кусочек рулета

So the comma is required just like in English when you have something like:

• Whatever dessert you choose, I’ll still ask for...

Here всё равно means anyway, all the same, or regardless.

It reinforces the idea that the speaker’s decision does not depend on the other person’s choice.

So:

• я всё равно попрошу = I’ll ask for it anyway / I’ll still ask for it

It does not literally mean that everything is equal in some mathematical sense. In everyday Russian, всё равно very often means it makes no difference or regardless.

Попрошу is the future perfective form of попросить.

In this context, it means something like:

• I’ll ask for
• I’ll request
• in a café or restaurant context, often almost I’ll order

Russian often uses просить / попросить this way when talking about asking for food, a portion, an item, and so on.

The perfective verb попросить fits well because this is a single completed request the speaker will make.

So:

• я попрошу = I will ask for / I’ll order
• not ongoing, but one specific request

Хотя бы means at least.

It sets a minimum amount or minimum request:

• хотя бы одну слойку и один кусочек рулета = at least one puff pastry and one piece of roll

This suggests:

• the speaker wants no less than that
• possibly more, but this is the minimum

It can also make a request sound a bit softer or more modest, depending on context.

Because один has to agree with the noun in gender and case.

слойка

• feminine noun
• direct object, so accusative singular
• одна becomes одну
• noun also changes: слойка → слойку

So:

• одну слойку

кусочек

• masculine inanimate noun
• accusative singular
• for masculine inanimate nouns, accusative looks like nominative

So:

• один кусочек

That is why the two phrases look different.

Because after a noun like кусочек meaning a little piece / a piece, Russian usually puts the thing being divided in the genitive.

So:

• кусочек чего? = a piece of what?
• рулета = of roll

This is a very common pattern:

• кусочек торта = a piece of cake
• ломтик хлеба = a slice of bread
• чашка чая = a cup of tea

So один кусочек рулета literally means one little piece of roll.

The word order is natural and standard.

Russian often puts the whatever/no matter what clause first:

• Какой бы десерт ты ни выбрала, я всё равно попрошу...

That sets up the condition first, and then gives the main point.

You can often change Russian word order for emphasis, but this version is very natural because:

1. the concessive clause comes first
2. всё равно appears early in the main clause, where it clearly contrasts with that clause
3. the requested items come last, where the sentence naturally builds to them

So the order is not random; it helps the sentence sound smooth and logical.