The ornamental design for a pastacooker, as shown and described.
FIG. 1 is a perspective view of a pasta cooker;
FIG. 2 is a top view of the pasta cooker;
FIG. 3 is a front view of the pasta cooker;
FIG. 4 is a right side view of the pasta cooker; and,
FIG. 5 is a left side view of the pasta cooker.
The dash broken lines shown in the drawings are for purposes of illustrating portions of the pasta cooker that form no part of the claimed design. In connection with the pasta cooker, the rear portion and bottom portion of the pasta cooker are not visible during ordinary use and form no part of the claimed design.