Yes - cook the butter and flour together for 2 or three minutes over moderate heat, stirring pretty constantly. You MUST cook the flour or your finished product will be very “pasty”. Once you’ve cooked the butter and flour add the milk (or stock or whatever) gradually, bringing it to a gentle boil between additions so you can judge the consistency. Start with it quite thick and thin it in increments until it’s just slightly thicker than you want. Make sure it’s hot but not boiling when you add the cheese - shredded so it melts faster and a little at a time so you don’t have a huge clump to try and work in. Stir, stir, stir and once it’s all melted adjust your seasoning and add a little more milk to bring it to the perfect consistency if necessary. If it’s too thin don’t try adding more flour - that will bring you back to the glue stage you were trying to avoid in the first place.