Preheat oven to 375 F/190 C. Spray a small casserole dish with non-stick spray or oil.: The kitchen will fill with a warm, anticipatory scent as the oven approaches temperature, and setting the right heat ensures the chicken cooks through while the coating browns. A properly preheated oven yields even baking and prevents soggy coating. A common mistake is placing the dish in a cold oven, which lengthens cook time and leads to overcooked filling or underbaked coating.
Trim any visible fat from chicken breasts, then put them one at a time inside a heavy plastic bag and pound with meat mallet, or something heavy, until the chicken is as thin as you can get it. Don't worry too much about the shape or whether there are some loose pieces, you can tuck them in when you roll up the chicken.: The slight sizzle when the oiled dish meets the hot oven helps the bottom of the rolls develop a light crust. Proper greasing prevents sticking while allowing air to circulate under the rolls for even browning. Using too much oil can pool and steam the underside, so use a thin, even layer.
In a small bowl mix together the basil pesto, sour cream, and grated mozzarella.: You will hear a rhythmic thud as the mallet flattens the chicken and see the fibers loosen, which helps tenderize and makes rolling simple. Achieving an even thinness guarantees even baking and prevents undercooked centers. A typical slip is pounding too aggressively in one spot, tearing the meat; work from center out and check thickness frequently.
Prepare two bowls, one with the two beaten eggs and one with a mixture of the finely grated Parmesan and the Almond Flour.: The aroma of basil will lift immediately as you fold the components, and the mozzarella will begin to soften into the creamy mixture. This combination provides the melty ribbon of flavor inside each roll. Overmixing can make the filling too loose, so blend just until combined.
Use a rubber scraper to spread a thin layer of the pesto mixture over each chicken breast, stopping about 1/2 inch from the edge of the chicken.: The egg bowl should have a glossy sheen while the dry bowl should be powdery and homogenous. This setup creates a reliable assembly line for even coating. Putting too little in either bowl forces double dipping and inconsistent coverage.
Roll up the chicken breasts lengthwise and secure them with a couple of toothpicks.: As you spread, you will feel the chicken flex and the pesto create a visible green ribbon across the surface, leaving a clean edge so the filling does not ooze. That thin margin makes rolling tidy and keeps the filling inside. If you spread to the edge the mixture will escape during rolling and baking.
Dip each chicken breast roll first into the egg mixture and then into the Parmesan-almond flour mixture, patting it on so each chicken breast roll is well-coated with the mixture.: Rolling will compress the filling into a neat spiral, and the toothpicks act like gentle clamps keeping the roll intact while baking. The inside should feel snug not loose. If the roll is too tight it can split, and too loose will unroll in the oven; aim for a firm but comfortable tuck.
Put chicken breasts into the casserole dish, season with fresh ground black pepper, and bake until the chicken is firm and lightly browned.: You will notice the coating change from glossy to textured as the egg acts like glue and the dry mixture adheres. This layered coating crisps and browns in the oven for contrast against the soft filling. A common error is letting the roll sit too long before baking, causing the coating to detach; work briskly from dip to dish.
Some chicken breasts sold in U. S. stores have added water. If there is some water in the bottom of the baking dish after the chicken has baked for a while, just spoon it out and discard.: As the dish bakes you will hear a gentle bubbling and smell nutty Parmesan as the coating browns. Check for a firm, springy texture and a faint golden color on the crust to know they are done. Overbaking dries the interior, while underbaking leaves the center soft; aim for a firm feel and light color rather than relying only on time.
Serve hot.: During baking you may see liquid collect, and removing it prevents the rolls from stewing in excess moisture, allowing the coating to stay crisp. Skimming this off improves texture and concentrates flavor in the remaining juices. Leaving the liquid can result in soggy undersides and diluted flavor.
Serve hot: The final moment is a warm presentation when steam lifts and the filling peeks through slightly, inviting immediate tasting. Cutting into a roll reveals the green pesto ribbon and melted cheese, and the first bite should be warm, moist, and fragrant. Waiting too long cools the cheese and changes texture, so plan to serve promptly for the best experience.