Short reply:
Recommendations:
- Leave your recipe amounts as written.
- Stabilize the whipped cream with gelatin (google Cook’s Illustrated stabilized whipped cream for recipe).
- Use a stabilized peanut butter (like Jiff) and cream cheese (like Philadelphia brand).
- Use chilled ingredients.
- Start by whipping a small amount of peanut butter into the cream cheese.
Detailed explanation if you’re interested in how I got there…
Below is a breakdown of the ratios using the cream cheese as the base on which other ingredients are calculated. Note the amount of whipped cream (by weight); it is significantly more than both sugar and cream cheese. It’s also considerably more heavy cream that an average cream cheese icing. Given the amount of cream, introducing oil from peanut butter could be a problem as both heavy cream and cream cheese contain a lot of water.
Whipped cream is very unstable; it begins to release its water immediately after being whipped. The released water and the oil in peanut butter will mostly cause the emulsion begin to break after sitting for an hour or so. Given the amount of heavy cream, I would first try a gelatin stabilized whipped cream. If you can control the rate of free water seeping out the emulsion, you have a better change of the emulsion holding. Cook’s Illustrated has a post online for using gelatin to stabilize whipped cream.
Start with a small amount of peanut butter. Whip a 1/4 cup to 1/3 cup into the cream cheese.
The natural water in cream cheese needs to be considered as well. In the US, the FDA allows up to 55% moisture in cream cheese. That high moisture content is one of the reason stabilizers are added to cream cheese. Assuming you’re in the US, I’d use Philadelphia brand cream cheese as it is stabilized. I would not use reduced fat or neufchatel as both will contain less fat and notably more moisture. So even without changing the amount cream cheese, by changing the type of cream cheese, you could introduce more water.
I mentioned earlier a regular peanut butter would be best as they contain stabilizers to keep the oil from separating. The less free oil from the peanut butter floating around, the better given the potential of water release from the cream and cream cheese.
Maybe use cold ingredients as well since heat will trigger water separation from the whipped cream and cream cheese, and oil from the peanut butter.
As I said, I’ve never made a peanut butter cream cheese icing, so this is just how I would think my way through the process. Please let us know how it turns out. Now I seriously want a PB&J and banana sandwich on toast
Ratios from original recipe
Cream cheese 1.00
8 oz = 226g
Sugar .66
1 cup = 200g; recipe calls for 3/4 (.75) cup
200 x .75 = 150g sugar
150g sugar/226g cream cheese = .66
Heavy Cream 1.60
1 cup = 240g; recipe calls for 1-1/2 (1.5) cups
240 x 1.5 = 360g
360g heavy cream/226g cream cheese = 1.59 (round up to 1.60)