You followed the recipe, set the timer, and the tops of your biscuits look pale and perfect. Then you lift one and the underside is dark brown, verging on black. It’s one of the most common baking complaints, especially once the Christmas biscuit season gets going, and there are usually only a handful of causes.

1. Your tray is dark and thin

This is the big one. Dark, non-stick baking trays absorb more heat than shiny ones, and thin trays pass it straight through to whatever’s sitting on them. Put those two together and the bottom of a biscuit cooks far faster than the top. A lot of the trays that come with ovens, or in cheap bakeware sets, are exactly this.

2. The tray is too low in the oven

Many ovens run hotter near the bottom element. If your tray’s on the lowest shelf, move it to the middle. If you’re baking two trays at once, swap them halfway through.

3. Your oven’s running hot

Ovens can run noticeably hotter than the dial says. If you’ve changed tray and shelf and still get dark bottoms, an oven thermometer will tell you quickly whether it’s the oven. We’ve covered how to check your oven’s real temperature separately.

The fix I’d try first

Swap to a light-coloured, heavier tray. The Nordic Ware Naturals Half Sheet (2-pack) is a well-known one, sold as commercial-quality bakeware. It’s pure, uncoated aluminium, which spreads heat evenly across the whole surface rather than concentrating it, and the pale finish doesn’t soak up heat the way a dark tray does. Biscuits brown gently and evenly instead of scorching underneath.

The rim has a galvanised steel rod encapsulated inside it, which is what stops it warping and popping with a bang in a hot oven. Outside it measures roughly 17.9 by 12.9 inches (about 45 by 33cm), so measure your oven before ordering. It suits most standard UK single ovens, but compact ones can be a squeeze.

A couple of honest caveats. Raw aluminium isn’t non-stick, so line it with baking paper or a silicone mat for biscuits. It also discolours over time, which is purely cosmetic, and it’s hand wash only, as the dishwasher will dull and mark it. Acidic things like tomatoes can react with bare aluminium too, so line it when you’re roasting those.

One last trick

If you’re stuck with your old dark tray for now, stack two together. The air gap between them slows the heat getting through to the bottom of the biscuits. It’s not as good as a proper tray, but it’ll get you through tonight’s batch.