Annie Bell's Key Lime Pie

Sweetness and bite: this easy-to-make pud has a creamy lime filling, biscuit base and light-as-air meringue topping.

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   1. You will need a 20cm loose-bottom cake tin 9cm deep and a baking sheet.
   2. To make the pie crust, reduce the digestive biscuits to a crumb-like consistency either using a food processor or by placing them in a plastic bag and crushing with a rolling pin. Transfer to a bowl, add the melted butter and toss until the crumbs are evenly coated. Now press the mixture on to the sides and base of the cake tin using your fingers, taking the mixture about 4cm up the sides, and then into the base. Press the mixture down and level the top of the sides as neatly as you can using a spoon.
   3. Preheat the oven to 190C/170C fan/ 375F/gas 5. Combine the lime juice and zest with the condensed milk in a bowl, whisking until you have a smooth, thick cream. Whisk in the egg yolks.
   4. Using an electric hand whisk, whip the egg whites and cream of tartar in a large clean bowl until risen. Gradually sprinkle over the sugar a tablespoon or two at a time, whisking well with each addition until you have a glossy, stiff meringue. Fold a fifth of the meringue into the lime base and pour this on top of the biscuit crust.
   5. Spoon the remainder of the meringue in mounds on top, taking it to the edge of the tin and covering the surface. Place the tin on the baking sheet and bake the pie in the oven for 30 minutes, by which time the surface of the meringue should be lightly golden and crusty and the lime filling set. Remove from the oven and leave to cool.
   6. Run a knife around the pie to loosen the sides and remove the collar. The pie is at its best eaten the day it is made. If you do chill it in the fridge, bring it back to room temperature before serving.