With the rack in the middle position, preheat the oven to 180°C (350°F). Butter and flour 3 13 x 23-cm (5 x 9-inch) loaf pans.
In a bowl, combine the flour, baking powder and salt. Set aside.
In another bowl, cream the butter and sugar with an electric mixer. Add the eggs one at a time, beating until the mixture is light and creamy. Add the vanilla.
With the mixer set to low speed, add the dry ingredients, alternating with the milk.
Bake until a toothpick inserted in the middle of a cake comes out clean, 40 to 45 minutes. Let cool partially and unmould. Place on a cooling rack until completely cooled.
Cut a slice about 1.5 cm (1/2 inch) thick from the long side of one of the cakes. Trim the edges of the cakes to form perfectly straight-sided rectangular blocks. Using a 2.5-cm (1-inch) round cookie cutter, cut 16 discs out of the reserved slice. Set aside.
In a bowl, cream the butter and vanilla using an electric mixer. With the mixer on low speed, slowly add the sugar. Beat until smooth. Divide the icing among 3 bowls. Stir enough of a different food colouring into each bowl of icing to give it a Lego-like colour.
Using a spatula, ice each cake with a different coloured icing. Smooth the icing as much as possible.
On a large rectangular serving plate or cardboard cake liner, arrange 2 cakes in an L shape. Place the third cake on top, straddling the other 2 cakes.
Ice the cake discs with the appropriate colour icing and arrange them on the cakes so that they resemble Lego blocks.
For one cake 310 ml (1 1/4 cups) unbleached all-purpose flour, sifted 5 ml (1 teaspoon) baking powder 1 pinch salt 125 ml (1/2 cup) unsalted butter, softened 250 ml (1 cup) sugar 2 eggs 5 ml (1 teaspoon) vanilla extract 125 ml (1/2 cup) milk
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.