Cakes & pastry
Sour Cream Custard Frosting
Sour cream custard frosting is made in two stages: cook sour cream, eggs, sugar and flour into a thick base, then cool it and beat it into soft butter. The base must leave a clear whisk trail before cooling. Adding a warm custard to butter or stopping the cooking too soon can leave the frosting loose.
4 min read
A cooked filling with a tangy flavour
This cream is richer than plain sweetened sour cream because it contains a cooked flour-and-egg base and whipped butter. It can fill honey or sponge layers and gives a different texture from cream cheese frosting.
The water bath provides gentler heat, but the mixture still needs constant stirring and enough cooking time. Set up a heatproof bowl over a pan so the bowl does not touch the water. Have a shallow cooling container ready before you begin.
Use the honey-layer method when planning a Medovik-style dessert.
Cook the base and combine with butter
Sour cream custard frosting
Ingredients
- 350 g sour cream; approximately 26% fat is a useful starting choice
- 120 g sugar
- 2 eggs
- 45 g wheat flour
- 130 g unsalted butter, 82–82.5% fat, softened
- to taste vanilla
Method
- Mix the base. In a heatproof bowl, combine the sour cream, sugar, flour and vanilla. Add the eggs and whisk thoroughly until no dry flour pockets remain.
- Cook over a water bath. Set the bowl above gently simmering water without touching it. Stir continuously, scraping the bottom and edges, until the base is thick enough to leave a whisk trail. Allow at least 15–20 minutes as a guide and ensure the flour is fully cooked.
- Cool the custard. Transfer to a clean shallow container, cover the surface and cool promptly until it is no longer warmer than the softened butter.
- Whip the butter. Beat the soft butter until pale and fluffy, approximately 4–5 minutes. Around 21°C (70°F) is a useful working point, but it should be pliable rather than oily.
- Combine gradually. Add the cooled custard to the butter a tablespoon at a time, beating until each addition is incorporated. Scrape the bowl and finish with a smooth, uniform cream.
The 15–20-minute cooking period is not a universal timer: bowl size, heat and batch depth affect how quickly the flour cooks and the base thickens.
Cook out the flour before cooling
A warm mixture that is only slightly thicker than at the start is not ready. The whisk should leave a visible trail, and the base should have a consistent thickness rather than a thick layer at the bottom with a thin liquid above it.
Stir through the entire bowl, including the edge nearest the pan. A sturdy whisk and a stable bowl make this easier. Keep the water gently simmering and check that it has not boiled away.
Flour must be fully cooked or it can leave an unpleasant raw taste. Adding more butter later does not correct an undercooked base. Likewise, a scorched flavour cannot be removed by masking it with vanilla.
Match the custard and butter temperatures
The butter and custard should both be at compatible, workable temperatures. Warm custard can melt the butter; very cold custard can make the butter form small pieces. Add the base gradually so each spoonful can disperse.
If the cream looks curdled, pause and feel the outside of the bowl. Correct a too-cold or too-warm mixture gently rather than adding more flour, sugar or butter. Letting the emulsion come together is a different task from thickening the cooked base.
The fat level and thickness of sour cream vary by product. A higher-fat product often gives a rounder flavour, but acidity is not determined by fat percentage alone. Use a plain product with a flavour you like.
Flavour lightly and keep the filling chilled
Vanilla paste, vanilla seeds or a little citrus zest can flavour the cream. If using an extract or spirit, add a small amount and assess the consistency; a large unmeasured liquid addition changes the formula. Gel food colour can be used sparingly when a coloured finish is needed.
Spread between fully cooled cake layers and chill the assembled dessert. The butter makes the cream firmer in the refrigerator, so allow only a brief controlled tempering for serving. Keep unused cream covered and refrigerated.
Measure the filling between layers if you want a level cake and a consistent cut. Reserve the exterior quantity before using the whole batch inside.
Common questions
Why is my frosting too loose?
The base may be undercooked, or it may have warmed the butter. Check the cooked thickness and component temperatures before changing the recipe.
Can I cook it directly in a saucepan?
This version uses a water bath for gentler heating. Direct heat needs a different level of control and can catch more easily.
When do I add the butter?
Whip the butter separately, then add the cooled custard to it in small spoonfuls.
Can I use it with honey cake?
Yes, it is a suitable style of cooked filling for honey layers. Plan enough cream and allow the assembled cake to rest chilled.