Dense fudgy brownies under a smooth chocolate ganache, finished with the flat multicoloured sprinkles that make them recognisable.

They are a copy of a supermarket snack cake, and the homemade version wins on both texture and chocolate, which is not a difficult contest.

Flatten the top while it is warm

This is the trick that makes them look right rather than homemade, and it takes ten seconds.

When the brownies come out of the oven and are still warm and pliable, press the surface lightly with the flat bottom of a metal measuring cup. It smooths out the domed centre and any lumps, and leaves a level surface for the ganache.

Ganache poured onto an uneven brownie pools in the low spots and runs thin over the high ones. Flat top, even layer.

Light pressure. You are levelling, not compressing.

Melt the butter and chocolate together, off high heat

Butter melted first over low heat, then six ounces of chopped chocolate stirred in until smooth, then the heat off entirely.

Low heat throughout. Chocolate seizes when overheated, and the milk solids in butter scorch. Melting the butter first gives the chocolate something to melt into rather than sitting directly against the hot pan.

The ingredient list says semisweet and the method mentions bittersweet. Either works and the difference is a few percent of cocoa solids. Semisweet gives a slightly sweeter result, bittersweet slightly darker.

Whisk the sugar in while it is warm

A minute or two, until the mixture is glossy and combined.

Warm is the important part. Sugar dissolves into warm fat far more readily than cold, and dissolved sugar is what produces the thin shiny crust that a good brownie has on top.

Undissolved sugar gives a grainy texture and a dull surface. If it still feels gritty when you rub a little between your fingers, keep whisking.

Eggs one at a time, then the yolk

Two whole eggs added individually, then the extra yolk and the vanilla.

The extra yolk is doing what an extra yolk always does: adding fat without adding water or more protein structure. That is what makes these fudgy rather than cakey.

The batter should thicken slightly and go smooth as the eggs go in.

Fold the dry in three batches

Cocoa, flour and salt whisked together separately, then folded into the wet mixture in three additions until no dry streaks remain.

Three batches rather than all at once, and folding rather than beating. Brownies have enough flour to develop gluten if you work them, and gluten is what turns a fudgy brownie cakey.

Stop the moment the streaks disappear.

Twenty four to twenty eight minutes at 325F

Until the edges are set and a toothpick in the centre comes out with moist crumbs.

Moist crumbs, not clean. A clean toothpick means overbaked, and an overbaked brownie is dry and crumbly rather than fudgy. The lower oven temperature is deliberate too; 325F bakes them more gently and keeps the centre soft.

Cool completely before the ganache

Fully cool, in the pan.

Ganache poured onto warm brownies melts and soaks in rather than sitting as a distinct layer. You would lose the two-tier look entirely.

For the ganache, heat the cream until steaming but not boiling, pour it over the chopped chocolate, wait one to two minutes, then whisk smooth. If it has not fully melted, five to seven seconds in the microwave finishes it.

Setting and slicing

Ganache spread level, sprinkles on top, then left to set before slicing.

Thirty minutes in the fridge speeds it up. In a hot or humid kitchen it may not set properly at room temperature at all, so the fridge is the reliable route in summer.

The classic shape is a rectangle with a line scored down the middle. Cut the slab in half, score each half, then cut each into four rectangles. That gives eight large ones, or sixteen squares if you would rather smaller portions.

The parchment overhang

Line the pan with parchment leaving an overhang on two sides. It is the only practical way to lift a slab of brownie topped with set ganache out in one piece, and cutting in the pan drags the ganache and ruins the edges.

About the sprinkles

The flat oval multicoloured sprinkles are what make these read as the original. Regular round rainbow sprinkles work and look slightly different. Add them while the ganache is still soft so they anchor rather than sitting loose.