Ermine frosting, sometimes called roux frosting or flour frosting, is made by cooking flour, sugar, and milk. Never heard of it? I hadn't either, but it's actually a super light and fluffy frosting (that does NOT taste flour-y at all) that reminds me of sweet whipped cream. You are going to love this unique frosting!
Add the flour, sugar and milk to a pan. Cool over medium heat while whisking constantly until thick like pudding, about 10 minutes.
Remove from the heat and add to a heat-proof bowl or quarter sheet pan. Cover with plastic wrap so the plastic touches the top of the mixture and prevents a film from forming. Chill in the fridge for 40 minutes
Add the room temperature butter to a stand mixer and whip with the whisk attachment for about 8 minutes, until the butter is light and fluffy.
Add the flour mixture to the butter one scoop at a time until it is all incorporated
Scrape down the sides and bottom of the bowl and switch to the paddle attachment. Add the vanilla and salt and beat on medium-high for 10-13 minutes, until smooth and fluffy.