What is the effect of substituting EVOO for butter when making a roux? Or some other oil? Further, for recipes that start with butter (generally sauteeing and building from there and at some point adding flour) will a substitute oil work just as well? For example, two of the recipes I have in mind are Lobster Thermidor (either the Rogov/Child 6 step recipe or Chef Louis DeGuoy's 1941 recipe) and a Baked Seafood Au Gratin (which calls for butter mixed with flour). If so, to what extent would the flavor and consistency be affected? Would I use equal portions of some other oil as butter?
FWIW, there are two reasons I want to do this: 1) I want to eliminate trans fats from my diet and 2) As weird as it seems, I don't really care for the taste of butter unless it's disguised (with sugar, for example).
Thanks for your help.