This is one of three styles of hand coverings included in HeartStrings’ Fine Filigree Fingerlings pattern.
In the Filigree Mitts shown here (leftmost in top photo, and detail of thumb gusset in lower photo), the Lace Filigree motifs are are extended to cover more of the hand, and the design includes a thumb gusset. These fingerless mittens are a flattering alternative to wearing mittens or gloves.
You can whip stitch across the top edge at each side of the thumb gusset to create a thumb hole if you wish to.
Stitch instructions: written
From the pattern description: Here are three styles of beautiful hand coverings styled for under-the-cuff wear to give the look of layering. The Lace Filigree pattern stitch might appear complicated to knit, but is surprisingly simple!