Line your pan. Place mini muffin liners in a mini muffin tin (about 18–24 cups).
For full-size cups, use a regular muffin tin with liners.
Melt the chocolate. Add 1 1/2 cups chocolate and 1 1/2 tablespoons coconut oil to a heatproof bowl. Microwave in 20–30 second bursts, stirring each time, until smooth. Or melt over a double boiler on low heat.
Don’t overheat—warm and glossy is perfect.
Make the filling. In a small bowl, combine 1/2 cup seed butter, 1–2 tablespoons maple syrup, 1/2 teaspoon vanilla, and a pinch of fine sea salt. Stir until creamy. If too thick, loosen with 1–2 teaspoons warm water; if too runny, add 1–2 teaspoons cocoa powder or a spoon of oat flour to firm it up.
Build the base. Spoon about 1 teaspoon melted chocolate into each liner and tilt the pan to coat the bottoms.
Chill for 5–10 minutes until just set but still slightly tacky.
Add the filling. Scoop 1/2 to 1 teaspoon of the seed butter mixture onto each base. Gently press to flatten slightly, keeping space around the edges so the top layer of chocolate can seal.
Top with chocolate. Cover each center with another 1–1 1/2 teaspoons melted chocolate. Tap the pan on the counter to level the tops and release air bubbles.
Finish and set. Sprinkle with flaky salt if using.
Chill for 20–30 minutes until firm.
Serve. Peel off the liner and enjoy straight from the fridge or let them sit for 5 minutes for a softer bite.