Assimil Dutch is an amazing course! It brings you to B2 in about 45 hours of applied study (just doing as the instructions tell you!) I really like Assimil courses in general but the polyglot community widely believes that the Dutch course is their best of all.
You can also find it online, but be sure to find the audio files also. They are essential. Each of the 100+ lessons are like this: After rereading the lesson text with the notes until you can read it without assistance - you then listen to the audio until you can understand the audio without reading the text, then you say it out loud until you can say it at the same speed as the audio without difficulty. So half of the course length involves the audio.
Good luck!