One of the few must haves in the kitchen is a mixing bowl; and size does matter in this case. The larger the better! Why? mostly because while mixing, things seem to fly out of the bowl quite easily. If you have to carefully fit everything in a small bowl and mix it gingerly, its not going to get mixed well now is it? Mixing bowls are extremely versatile, I use them for making cookies/cupcakes, mixing loose doughs, mixing salads, storing dough in the fridge. I have ones which are glass and are microwave friendly, so I frequently use them for melting chocolate. I also have ones which are steel and are particularly suited to cool rapidly. That is needed to make whipped cream.
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