Combine sugar and flour in a saucepan and cook at medium heat for 2 minutes. Then, slowly add the milk and cook for a further 3-5 minutes until the mixture thickens like a pudding.

Place this paste into a shallow bowl and cover the entire surface with plastic wrap to avoid skin forming on top. Let it come to room temperature.

Then, soften your butter. Buttercream can only be made with the right temperature butter that is neither cold, nor soft or runny.

Prepare a stand mixer with the paddle attachment. Alternatively, use your electric hand mixer.

Cream the room-temperature butter at medium-high speed for 3 minutes until it becomes light in color and fluffy in texture.

Then, add the room temperature paste into the butter in 4 batches, then whip it for another 4 minutes or until the mixture becomes light, fluffy, and increases in volume

Lastly, add the vanilla extract and salt and continue whipping for another minute until it is smooth and silky.

At this point, the Ermine frosting should have the perfect pipeable fluffy texture. If, for some reason, it is too thin, place it in the refrigerator for 30 minutes.

Note that the buttercream texture is best when the butter is at the right temperature (room temperature), and the mixture is freshly whipped. I like to use the frosting immediately or store it at room temperature in a piping bag for a few hours. If stored in the refrigerator, you will need to bring it back to room temperature before using it and might need to give it another minute or two to whip in the stand mixer to increase the volume again.