Although I followed the Coffee and Walnut Layer Cake recipe perfectly, and used 2 x 20-inch sponge tins and measured batter into tins, my oven looks like a volcano. I have turned oven up to 180°C although it's a fan as even after 20 minutes the cakes looked very raw. Will see what it tastes like, but I'd like to try again another day.
Nigella's Coffee And Walnut Layer Cake (from KITCHEN) is a Victoria sponge variation, enriched with ground walnuts. It usually bakes well to give two even sponges. We assume that from the description the cake batter may have flowed up and out over the sides of the tin. It is possible that the sponge tins were slightly too shallow - the cake batter should come no more than halfway up the sides of the tin. If the tins are too shallow you can line the sides of the cake tins (on the inside) with baking parchment (parchment paper), with the parchment coming above the edge of the tin to make a collar.
Sometimes when cakes overflow it is due to too much raising agent. The recipe uses 2½ teaspoons of baking powder and ½ teaspoon of bicarbonate of soda (baking soda). Use a 5ml teaspoon and 2.5ml half teaspoon to measure the amounts, using level spoonfuls. And be sure not to get the baking powder and bicarbonate of soda the wrong way around, as bicarbonate of soda is very active and will cause the cake batter to bubble up a lot in the oven.