Could I substitute peanut butter in place of butter or crisco for cookies?

sometimes i'll replace 1/2 the butter in my cookies with peanutbutter and will cut the sugar a little. they still turn out pretty well. replacing all the butter would be bad, but some of it won't make much of a difference.

Shortening and regular butter don't work the exact same in a recipe. Sometimes it has to do with cookies spreading, humidity, etc. I've though used peanut butter for regular butter/margarine in recipes and haven't had any issue. I prefer the added flavor it gives. Do a small batch test run. Good things have often been discovered via experimentation.

The simple answer is no, it wouldn't work.

Vegetable shortening is 100% fat. Peanut butter contains significant amounts of protein and starch, and carries a profound peanut flavor. These are going to drastically change any recipe it is used in lieu of shortening.

If you desire lower fat recipes, I suggest you look specifically for recipes designed with that aspect in mind.

See also:

• What are some low fat butter substitutes for cookies?
• Are there low-fat substitutes for shortening in baking?

Melting Point

Melting point is typically only significant in baking in two circumstances:

• Use of the creaming method where sugar is cut into fat incorporating air as part of the leavening process
• Making of laminated doughs such as puff pastry, croissants, or strudels

Peanut butter is a complex food, but the oil phase is either already liquid (in room temperature so-called "natural" peanut butters, or only contains a small amount of saturated fats in typical commercial peanut butters, and so has a lower melting point that pure hydrogenated vegetable shortening.)

Neither of these typically apply to cookies.

Consistency

Consistency is harder to predict. It depends on what is being cooked, but peanut butter has less fat than shortening (since shortening is pure fat, and peanut butter has a high percentage of peanut solids, starches and proteins for the most part).

The interaction of these various components in the chemistry of the actual product will determine the consistency.

During the second world war my father and grandfather were bakers. Lard and most other oils were in short supply as they were used in the war effort to produce fuels and lubricants for the tanks, ship and other motorized vehicles. As a substitute in baking bread they used peanut butter but even it had most of the oils pressed out of it making it hard and dry. To remedy this they mixed condensed milk to the peanut butter to soften it and it worked. Today instead of making just a white bread we make a multi six grain bread using all natural peanut butter and condensed milk along with adding honey, sunflower seeds and walnut pieces.