Chocolate chip cookie layer cake

In a stand mixer, cream the softened butter alone for about 20 seconds until lump-free.

Add the granulated sugar, then the dark brown sugar, and cream well.

Add room-temperature eggs, ideally one at a time, then the vanilla extract.

Break up the baking soda lumps and mix it with the all-purpose flour and salt.

On low, add the dry ingredients in two additions; scrape the bottom and do not overmix.

Mix in the finely chopped bittersweet chocolate.

Divide the dough evenly between four floured and lined 9-inch pans, about 675 g each, and press it flat by hand. (Or shape 9-inch circles on parchment on baking trays, chilling the dough first.)

Sprinkle with M&M's.

Cover each with cling wrap, with cling wrap between the stacked layers, and age in the fridge a few hours or up to three days.

Bake fan-assisted at 350F for about 20 to 22 minutes, until firm under a finger but still a little soft in the middle; do not overbake. Cool in the pans.

Smear frosting on the platter, set down a layer, and spread room-temperature buttercream generously out to the edges; repeat, best-looking layer on top, pressing down so the frosting peeks out the sides.

Serve straight away or hold at room temperature up to 12 hours.