If someone is not sure whether they will really need to cook on Yom Tov for Shabbos may they still make an Eruv Tavshilin *with* a bracha?
To answer briefly (before Yom Tov), somebody who might require the eiruv for cooking from Yom Tov to Shabbos, but is not certain that he will need to do so, can make the eruv tavshilin with a berachah.
According to some authorities, even somebody who does not require the eiruv for purposes of cooking can recite the berachah on the eiruv, because it gives him the ability to prepare (see Mo’adim U-Zemanim 7:122).
Most authorities do not agree, and rule that where a person has no intention of making use of the eiruv in preparing from Yom Tov to Shabbos, a berachah should not be recited (see Minchas Shlomo 2:53:2; Iggros Moshe, Orach Chaim 5:36; Minchas Yitzchak 7:36 and 9:54:3; Shemiras Shabbos Kehilchasa 31:35).
In our case, because the person involved reckons that he might need to prepare from Yom Tov to Shabbos, the chance that the preparation will be required is sufficient to render the eiruv “necessary” (he needs it for he might need to prepare for Shabbos), and therefore a berachah is recited.