Homemade Peanut Butter Cups

Line two baking sheets with 48 regular-size paper muffin liners or 96 mini paper muffin liners; set aside.

Beat the peanut butter and butter on medium in the bowl of a stand mixer fitted with a paddle attachment until smooth and creamy, about 2 minutes. With the mixer on low, gradually stir in the powdered sugar, graham cracker crumbs, vanilla extract and salt. Beat until well combined, about 1 minute.

Divide the peanut butter mixture into 1 1/2 teaspoon balls for regular size peanut butter cups or 1/2 teaspoon balls for mini cups. Flatten into about 1 1/2-inch wide discs for regular size or 1-inch wide discs for mini cups. Place on a parchment paper-lined baking sheet and chill while melting the chocolate.

Fill the bottom of a medium saucepan with about 1 inch of water and bring to a simmer over medium-high heat. Place chopped chocolate in a dry, heatproof glass or ceramic bowl that is slightly larger than the saucepan. The bowl should sit on top of the pan without its bottom touching the water.

Reduce the heat to medium-low. Place the bowl of chocolate over the saucepan of water. Heat the chocolate, stirring occasionally with a dry rubber spatula, until chocolate is mostly smooth and melted, 8 to 10 minutes. Remove the bowl from the saucepan and continue stirring until the residual heat melts the remaining chocolate and mixture is smooth (return bowl to saucepan, if needed).

Spoon about 2 teaspoons of chocolate into the bottom of each regular muffin cup or about 1 teaspoon chocolate into the bottom of each mini muffin cup. Gently press 1 peanut butter disc into each muffin cup, allowing the chocolate to come up around the sides. Spoon chocolate on top of peanut butter to cover, about 2 teaspoons for regular muffin cups or 1 teaspoon for mini muffin cups.

Sprinkle the top of each peanut butter cup with flaky sea salt, if desired. Chill peanut butter cups until chocolate is set, about 1 hour.