Goidsargi Estibaliz Carranza Zabala, who has both Spanish and Mexican citizenship, appeared in a Viennese court amid a sea of publicity surrounding the grisly murders.
Prosecutors allege in 2008 the woman shot her husband three times in the head as he worked at his computer and then dissected his remains with a chainsaw. She apparently stored her husband's body parts in tubs in a freezer for a few months before putting them in the floor of her Vienna shop.
Two years later, prosecutors charge, she took the same Berretta .22 pistol to her lover as he slept after she found out that he had been seeing another woman. He also ended up in bits in the floor of the ice cream parlour.
The body parts were found by accident by builders during renovation work in 2011. Carranza went on the run despite being two-months pregnant but was captured in Italy and later extradited.
Prosecutor Petra Freh described 34-year-old Carranza as a "cold and extremely dangerous woman" who had a "unique" personality.
"Let us make no mistake," she continued. "During the course of this trial we have to remember that this woman killed twice. She is a ticking time bomb." Psychiatrist Adelheid Kastner, who once examined Josef Fritzl, deemed Carranza fit for trial despite suffering from mental problems.
"She suffers from a personality disorder, she has serious mental and psychological abnormalities," Doctor Kastner wrote in her report. "It has to be feared that the woman could commit further acts with serious consequences."
Defence lawyer Werner Tomanek told the AFP news wire that Carranza "intends to confess" in court.