The phrase "and fold in a" is correct and usable in written English.
It is typically used in cooking or baking instructions to indicate the gentle incorporation of ingredients into a mixture.
Example: "After mixing the dry ingredients, add the whipped cream and fold in a third of it until just combined."
Alternatives: "and gently mix in a" or "and incorporate a".
I beat together the eggs, yolks and sugar until pale (and thus also rather fluffy, although she doesn't mention this) and then beat in the melted butter and chocolate and fold in a negligible amount of flour.
To make the fritter batter, simply combine the clam meat and juice with flour, egg yolks, baking powder, spices and corn, and fold in a few stiffly beaten egg whites.
We should enjoy, then, a sport in which the same set of batsmen can hang around all week in some conditions and fold in a day in others; in which the same group of bowlers can rage against the lack of help in some pitches, then resemble world-beaters on others.
We speculate that the existence of cooperative hidden folding intermediates in small proteins could be the consequence of the highly specific structures of the native state, which are selected by evolution to perform specific functions and fold in a biologically meaningful time scale.
Add these pieces up and fold in a near $7 billion stake in Industrial and Commercial Bank of China and some other investments held directly on the Goldman balance sheet, and their value already exceeds the firm's $55 billion market capitalization.
Two giant resin bar counters in its molecular-tapas Arola Restaurant bend and fold in a fashion similar to the melting watch in Dali's The Persistence of Memory.
It's a salad made with pale green fennel, shaved super-thin on a mandoline so that it curls and folds in a tall mound on the plate.
Flavodoxin adopts the common repeat β/α topology and folds in a complex kinetic reaction with intermediates.
By placing the seams and folds in a specific way, he actually emphasized the roundness of a child's body.
What had been a lump of dirty laundry is returned to the player clean, pressed and folded in a box.
A recurring theme in Pitt's table designs is the substitution of conventional legs for one continuous line of structure, a single strip that undulates, bends and folds in a contorted 3D doodle.
