Heat your oven to 400°F/200°C. Line a baking sheet with parchment. Keep pastry chilled until ready to roll—warm pastry equals mushy, not flaky.
In a bowl, combine sausage meat, grated apple (lightly squeezed), onion, garlic, herbs, mustard, breadcrumbs, salt, pepper, and optional spice. Mix gently until just combined. Overmixing = tough texture.
Pinch off a teaspoon of filling, microwave for 20–30 seconds or pan-fry. Taste and adjust salt/pepper. It's your only shot before baking.
On a lightly floured surface, roll the whole-wheat puff into a rectangle about 10×12 inches (25×30 cm). Slice lengthwise into two long strips.
Divide filling between the two strips and shape into long, even logs down the center of each strip. Leave space on either side for sealing.
Brush one long edge of pastry with beaten egg. Fold the other edge up and over the filling, then wrap to overlap the egg-washed side. Press gently to seal; use a fork for extra insurance.
Transfer the logs to the fridge or freezer for 10 minutes. This firms everything up and prevents squashing when slicing.
Cut each log into 10–12 bite-size pieces. Place seam-side down on the lined tray, spacing slightly.
Brush the tops with egg and sprinkle with seeds if using. For extra puff, chill again for 5 minutes. Yes, it matters.
Bake 20–25 minutes until deeply golden and crisp, and the filling reaches at least 165°F/74°C. If bottoms aren't crisp, give them 3–4 more minutes.
Let them sit for 5 minutes so the juices settle. Serve warm with mustard, apple chutney, or a tangy yogurt dip.