Place pork schnitzel on a clean work surface and pound gently until flattened. Season both sides with salt and pepper.
In a shallow bowl, whisk together the egg, cooking cream, heaped horseradish, and heaped mustard until well combined.
Set up three shallow bowls or plates: one with flour, one with the cream mixture, one with breadcrumbs. Coat each schnitzel lightly in flour and shake off excess, dip both sides into the cream mixture, then press both sides into the breadcrumbs until well coated.
Heat the clarified butter in a large frying pan over medium-high heat until shimmering. Working with 1-2 schnitzels at a time, carefully place them in the pan and fry for 3-4 minutes per side until golden brown and the internal temperature reaches 63°C (145°F). Do not overcrowd the pan.
Transfer the cooked schnitzels to paper towels to drain briefly. Serve immediately with fresh lemon slices.