This work analyzes and proposes solutions for subtle, but relevant, problems related to the EONIA curve calibration. The first issue examined is how to deal with jumps and turn-of-year effects. The second point is related to the problem caused by imperfect concatenation between spot starting OIS and forward starting ECB dated OIS: in order to avoid distortion, a meta-instrument called "Forward Stub" shoud cover the section between the maturity of the last spot starting OIS and the settlement of the first ECB OIS. Its implied value can be derived assuming a no-arbitrage conditions. The final issue is the empirical evidence that the forward overnight rates are generally constant between ECB monetary policy board meeting dates: because of this, a log-linear discount interpolation is a good fit. Anyway, flat forward rates are hardly realistic on the long end. This is the rationale to suggest the use of a "Mixed Interpolation" which merges two different interpolation regimes. All the algorithms used to perform the analysis are implemented in the open-source QuantLib project.