Design Hack: Faux Window Sill
An easy and effective way to create the illusion of a beefed-up window frame is to paint a trompe l-oeil sill. Search online for a style and profile that suits your space, then blow up the image to the appropriate size and print it. Make a stencil by tracing the printout onto a piece of foamcore and cutting it out using a utility knife. Position the stencil under your existing sill and outline the shape onto the wall with a pencil, then carefully paint out the area to match window trim.