Polish molds and prepare ingredients and workstation. Assemble your plastic bowl, chocolate, cocoa butter, silicone mat, etc. I use these polycarbonate molds and 250g of chocolate works great. However, the exact amount you need may depend on your molds. Note that silicone molds are not recommended because they retain heat and may mess with the temper. Your mileage may vary. Heat colored cocoa butter according to instructions and paint patterns on polished molds as desired.
Reserve 50g of couverture chocolate (needs to be tempered and stable). In a small plastic bowl, add 200g of couverture chocolate and microwave in 30 second increments until it reaches 45°C / 113°F, stirring well between each stint.
Once fully melted, add in 30g reserved chocolate (you may add up to 50g as needed). Continuously mix so the added chocolate melts via residual heat. The temperature should lower to 31°C / 88°F.
Quickly add chocolate to the molds, pouring into all cavities. Tap on the counter to remove air bubbles, then turn over on top of a silicone mat or parchment paper so the chocolate runs out, leaving each cavity coated. Allow to set for 8-12 hours.
Fill each cavity with biscoff nougat (there will probably be some leftover) to ⅝ full.
Repeat the tempering process above to cap the truffles. If able, use a heat gun to warm the edges of your cavities prior to tempering. Then temper the chocolate and pour over the cavities, scraping off excess. Allow to set for 8-12 hours, then remove from molds. If properly tempered, they should come out easily from the polycarbonate mold.