I highly recommend measuring by weight and mls instead of cups. You will get better, more consistent results!

• Chop the butter into cubes. Head a medium, light colored pan on medium.
• Add the butter and cook, stiring frequently until butter foams and goes brown and has a wonderful nutty aroma. This may take a few minutes. Watch it closely as it can brown and then burn quite quickly.
• Immediatly transfer to a heatproof container. Make sure you get all the brown bits at the bottom as that's where all the flavor is! Chill in fridge until butter solidifies. You need the butter at room temperature to make the frosting.
• Add the brown butter to a stand mixer or bowl, making sure you include all the brown bits at the bottom.
• Add the brown butter and Biscuff spread to the bowl of a stand mixer and beat together until smooth.
• Sift in the icing sugar and salt. Add the lemon juice and milk. Beat on medium until fluffy and well combined. Taste and check the texture. If it's too firm add another ½ tablespoon of milk and beat again. If it's too loose add another couple of spoonfulls of sifted icing sugar and mix well.
• Spread or pipe onto cakes and cupcakes and you're done!