½cup(85g)semisweet or bittersweet chocolate, chopped
Preheat oven to 350°. Line baking sheets with parchment paper or silpat liners.
Using an electric mixer, beat butter and sugar in a large bowl, occasionally scraping down sides of bowl, until smooth, about 2 minutes. Add egg and vanilla and beat to blend. Scrape down sides of bowl. Add the flour, baking powder, soda and salt. Mix. Stir in the oats, pecans and chocolate chips just until combined.
Scoop out about 1 1/2 tablespoonfuls of dough at a time and roll into balls. Place on a baking sheet about 2 inches apart. Press down on each dough ball until it is about 1/2-inch thick.
Bake the cookies for 9-11 minutes until lightly golden and set around the edges. Remove the cookies to a cooling rack to cool completely. Repeat with the remaining dough.
Up to an hour before serving, make the chocolate ganache for drizzling by placing the chopped chocolate and honey in a small bowl. Bring the cream to a simmer in a small saucepan or in the microwave (watch carefully so it doesn't scorch or overflow!). Pour the hot cream over the chocolate and let the mixture stand for 1-2 minutes before stirring. Whisk or stir until the chocolate is melted and smooth. Set aside.
Spread 1-2 tablespoons marshmallow creme on the bottom of half of the cookies. Top with the remaining cookies. Drizzle with the chocolate sauce and serve immediately. As I noted above, if the marshmallow creme is put on the cookies too far in advance, the cookies will slide around and the marshmallow creme can get extremely sloppy and gooey. I recommend assembling the cookies no earlier than 15-30 minutes before serving. If you have to do it farther ahead, they may not look as pretty but will taste delicious.
Make Ahead: the cookies can be made up to 2 days in advance and stored in an airtight container (yippee!).Assembling: I recommend assembling the cookies with the marshmallow creme as soon as possible to when you want to serve them as the marshmallow creme tends to get sloppy, extra gooey and leaks out of the cookie sandwiches.Presentation: if you absolutely need to assemble them earlier (like I did), prepare yourself that they may look messy but will taste absolutely delicious.