In a large bowl, beat together the butter and sugar until light and fluffy.
Add the eggs one at a time and beat well into the sugar and butter mixture.
Next, add the vanilla and the red food colouring. Beat into the batter.
Scrape down the bowl and add the following ingredients in this order: flour, baking powder, and salt. With the mixer on low speed, gently blend the baking powder and salt into the flour - just a few seconds.
Now, increase the speed on the mixer to medium and blend the flour into the batter just until the flour is incorporated.
Add the milk and fully incorporate.
Divide the batter into the prepared cupcake tins.
Bake for 18 minutes.
Remove from oven and allow to cool for 5 minutes. Remove cupcakes from tin and place on wire cooling rack to finish cooling.
For the Frosting:
Add the flour and milk to sauce pan. Cook over medium heat, whisking continually. It's important to slowly whisk to prevent the flour from clumping at the bottom of the sauce pan and to prevent the mixture from burning.
Allow the mixture to cook until it becomes very thick. It should look like a gloppy mess! Set it aside to completely cool.
Once cooled, whisk in the vanilla extract.
Next, in a large mixing bowl, beat together the butter and sugar until light and fluffy. Don't take any shortcuts - beat until the sugar is dissolved into the butter.
Transfer all of the flour and milk mixture into the butter mixture and beat until well combined. Beat until the mixture looks like whipped cream.
At this point, you can use a small spatula to frost the cupcakes, or transfer the frosting to a piping bag with your tip of choice. Once the frosting is applied, top with sprinkles.
Please note, this frosting does not harden. It will continue to stay soft, so do not stack the cupcakes when storing.
Notes
Cooking time does not include cooling and decorating.