Mix 1 1/2 cups brownie crumbs with 1 teaspoon milk only if the crumbs feel dry, adding the remaining 1 teaspoon milk when needed. Divide into 6 equal portions and press each into a firm 2 1/4- to 2 1/2-inch round. Alternatively, cut 6 rounds from a completely cooled, thin brownie slab.

Stir together 1/2 cup creamy peanut butter, 1/4 cup powdered sugar, 1/2 teaspoon vanilla extract, and 1 pinch salt until smooth. Divide into 6 portions, about 2 tablespoons each.

Microwave 1 1/2 cups chocolate in a dry microwave-safe bowl for 30 seconds, then stir. Continue in 15- to 20-second bursts, stirring after each one, until smooth. Add 1 to 2 teaspoons coconut oil only if the chocolate needs thinning.

Set 6 standard silicone muffin cups on a sheet pan or sturdy plate. Spoon about 1 tablespoon melted chocolate into the bottom of each of the 6 cups and tilt slightly so the chocolate reaches the lower edges.

Place 1 of the 6 brownie rounds over the chocolate in each cup, keeping a narrow chocolate border around every round.

Add 1 of the 6 peanut butter filling portions, about 2 tablespoons, to each brownie round. Flatten slightly or leave softly domed, keeping the filling away from the edges.

Divide the remaining melted chocolate among all 6 cups, using about 2 to 3 tablespoons per cup. Guide the chocolate down the sides so it meets the bottom layer, then tap the tray lightly to smooth the tops.

Refrigerate all 6 cups for 20 to 25 minutes, or until completely firm. Peel the silicone away from the chilled chocolate and let the cups stand for 5 minutes before serving.