Using the anisotropic Hall effect in a sub-micron lithographically well-defined two-dimensional electron system we measure the stray field of individual ferromagnetic nanoparticles in tilted magnetic fields. Our model calculations and experimental data show that one can map out the particle's hysteresis loop in great detail even if the field Happ is tilted away from the specimen's easy-axis by an angle φapp around 90°. The investigated Ni nanomagnets exhibit a well-defined remanent 'up'- and 'down'-state. For the angular-dependent switching we find two different regimes: below a critical angle φc, the hysteresis loop is irreversible and squared, for φc <φapp ≤ 90° it becomes partly reversible, but discontinuous jumps are still resolved. This characteristic switching behavior is found to depend on the nanomagnet's diameter.