Sauce béchamel. Sauce velouté. Whatever. I made my first one last night. I'd been given a recipe from our 'stock' of retained ones (those bits of magazines, newspapers, back of cereal packets that we hoard). Also additional instructions... It wasn't enough. It was the roux that took me by surprise. Add flour to hot butter and strange things happen. Heston is right to become curious about the chemistry. It was in a thick bottomed pan, copper sandwiched between stainless. It held a lot of heat. The butter sucked up the flour in one! Left me stirring madly avoiding burned butter. Julia Child said

"cook slowly, stirring until the butter and flour froth together for 2 minutes".

Is that a time limit? Or the time I'm to wait while it's frothing? Either way I was left with a dry(ish) number of balls of 'dough' from peanut sized up to a lump about 2 inches across! After a minute or so the balls started to sweat and soften. Something was happening. The objective is to rid the sauce of its floury taste. The 'something' was that the balls seemed to be softening? Was the surface bubbling? Not by my definition, but then I associate bubbling with liquids, not balls of butter/flour!

Sods law came into action then. I'd put the milk on the heat and ignored it for too long. As I was stirring frantically, the milk boiled over. My carefully measured 625mL decreased somewhat! Back to the roux.

I certainly didn't see any frothing. At this point the bottom of the pan (it was off the heat) was bothering me with the remnants of the flour starting to colour up. I chickened out around now. I'm guessing it was no more than two minutes. Seems French cooking has 'several minutes' for this stage. I'll try again and take it further. The roux is only 50gm butter / flour. Not a lot to waste for the sake of experimentation.

The dish was Lasagne Bolognese so I was using the sauce as a simple béchemal. At this stage Julia diverges from our recipe. Ours adds cold milk in small quantities. Julia heats the milk to boiling then adds it all - with the instructions to 'stir vigorously'. I tried a mix, possibly a mistake. The heat was clearly retained in the pan, the milk nearly exploded! Hissing and steaming frantically. I stirred that in, only to create a lumpy mess. More milk and it was hissing again. Let it cool first? Both the roux and the milk? Just the roux (or at least let the heat from the pan disperse a little). Suggested mixing implement is a whisk. IMHO that wouldn't get into the corners to loosen the roux 'lumps', so I used a wooden spoon. Tempted to use an electric whisk except for the same issue. I didn't succumb. Eventually emptied the last two thirds into the pan. Only then did I get time to mix it sufficiently (with a wire whisk) to get rid of the lumps. I'm guessing, but I think the heat from the pan was sufficient to thicken the mix. I almost didn't put the pan back on the heat. Not knowing how thick it should be I heated it for anothe minute, after which it had the consistency of fairly thick porridge. I judged that sufficient and left it at that, moving on to the rest of the recipe.

The finished product tasted as it should. One comment was that the liquid had almost separated (as in oil and water separating?) although if it did, it was minimal. Taste wise? I was happy.

How others do it

This shows a thick liquid, much more what I was expecting. Julias comments about foaming are right on the mark here. This guy mentions equal volumes of flour and butter though, not weight?

This method uses equal parts (volume again?). I like the idea of adding the roux to the milk (for the béchemal or velouté) after freezing. Makes sense to allow thickening to the desired level!

This guy (if you can see), has a 'paste' much like mine. Again the two minutes mix though

This one is off beat, using gluten free flour which makes me wonder, but again the 5th image has that 'paste' look! And that was after commenting that more butter was used than flour.

Yes. Excellent. Covers all the bases. The ratio of flour to butter (by volume), the pan (thick based), low heat. When to add the flour (when the butter has clarified (Stops foaming). How long to 'cook' the roux. Five minutes, but that over a low heat! He uses US 'half cup'. I.e. again by volume not weight. This for a béchamel btw. Note he also adds cold milk to the roux? In three parts whisking all the while. Then heats for ten minutes to finish it off