I love the Lavender Cupcakes from Domestic Goddess cookbook and have made them many times but not with the lavender. My kids love them too. So I want to make a whole cake with the recipe. Is that possible to just increase the ingredients?
The Lavender Cupcakes (from Domestic Goddess) are a variation of the classic cupcake recipe in the same book so we are not sure if you are just referring to the basic cupcake recipe. The good news is that the cupcake recipe is a fairly standard Victoria Sponge recipe and so you can double the quantities to make a 2-layer 20cm/9-inch sandwich cake. Alternatively follow Nigella's Victoria Sponge recipe in the same book (on p14), this recipe uses some cornflour (cornstarch) instead of plain (all-purpose) flour for a slightly more tender crumb.
If you are making a large lavender cake then again you can use one of the basic cake recipes above and reduce the vanilla extract to 1/4 teaspoon. Infuse the 125ml/1/2 cup milk with lavender, as directed in the cupcake recipe, and use 3-4 tablespoons of this to flavour the cake batter. We would suggest filling the cake with a vanilla buttercream and a complementary jam (in some plces you can buy blueberry lavender jam) and then icing the top with a glace icing made from about 200g/2 cups icing sugar (confectioner's sugar) and enough of the lavender milk to make a thick but spreadable icing.