When I was hunting for my last pattern for a pair of knit mittens, I wanted a pair of convertibles rather than straight up mittens or fingerless mittens. Unfortunately, I couldn't find any I liked... This is how I solved my pattern problem.
A pair of knit fingerless mittens (this time, I made "Owlings", by Kerrie James - the link will take you to it's Ravelry page)
A ball of the same or co-ordinating yarn
Appropriately sized double pointed needles (4)
A large eyed sewing/darning needle
You may also choose to attach a button to each mitten, to hold the flip-top in place.
Having taken a look at the Owlings pattern online, it appears that it is currently unavailable for download - you need to contact the designer for the pattern. Any simple fingerless mitten will work, although, for this particular set of instructions, I'd suggest something in a DK/light Aran (worsted) weight yarn, based on around 40 stitches CO. A simple but effective pattern would be something like Fetching, from Knitty.
Ready? Off we go...
Step 1: Set Up & Knit
Arrane the mitten in front of you, palm down, and work out a point on the mitten which will sit across your knuckles. This is where the flip-top will attach to the main body. Along this row, pick up 21 stitches on one needle and leave the needle in place. Call this needle one. Cast on 21 more stitches across 2 needles (2 and 3). Join these new stitches to the picked up ones, making sure that the stitches are not twisted and they are the right way up! To join the needles in the round, I slip the first stitch from needle 1 onto needle 3, and cross the last stitch from needle 3 onto needle 1, and then slip the last stitch on needle 1 to needle 2, and cross the first stitch on needle 2 back to needle 1. There's some pictures showing this.
I continued to knit in pattern for 18 rows - in this case, knit 4 purl 1 rib. Those of you keeping up with the maths will realise I made a small error here, and tried to fit a stitch pattern that takes 5 stitches into a cast on of 42, leaving me 2 stitches spare - I just increased one repeat on needle 2 and one on needle 3 to be knit 5 purl 1 instead, to get rid of the odd stitches. It doesn't look too funny (although I wish I'd worked it out better), and it's only a problem if you're knitting in pattern - if you knit the entire piece in stockinette (plain knit stitch all the way around), you won't have any problem.
18 rows of knitting brought the flip-top to the final knuckle of my middle finger - you may need to do more or less.I have quite short fingers though! Once it reaches that point, it's time to start making decreases and doing some shaping.
I worked the decreases on every other row, as follows. It should subtract 6 stitches by the end of each round.
R1 - Knit 5, Knit 2 together (K2tog) - repeat to end (36 remaining)
R2 - knit
R3 - K4, K2tog - repeat to end (30 remaining)
R5 - K3, K2tog - repeat to end (24 remaining)
R7 - K2, K2tog - repeat to end (18 remaining)
R9 - K1, K2tog - repeat to end (12 remaining)
R11 - K2tog - repeat to end (6 remaining)
R12 - K2tog - repeat to end (3 remaining)
Once you're down to the final 3 stitches, cut the yarn to around 6" (15cm) long. Thread the tail of yarn onto your darning needle, and pass the needle through the remaining 3 stitches. Removing the knitting needles, and pull tight. Push the needle through to the inside of the flip-top, and tie off through a couple of stitches. Weave the end into the knitted fabric, and trim. Thread the needle onto the cast on tail and weave this in to the main body of the mitten.
Repeat this process again for the second mitten - make sure you're working on the right side of it, otherwise you end up with 2 left/right mittens!
Step 2: Knitting Basics
I'm no knitting expert, but fingers crossed, these tips may help if you need it....
Picking up stitches
I find the best way to do this is to pick a side of the stitch (I work right - left, and always use the left "leg" of the stitch), and always pick up the same side as I go. This works best on straight rows of picking up stitches, but can be worked for verticals and more complex picking up. There's a photo or 2 explaining this on the previous step, and showing where I put the needle.
I can't explain this in words! I tried to create step by step photo instructions, but they weren't making much sense. Instead, there's a video here - not mine(!), but a very good link. The other video's on that website have always been very helpful to me.
With the working yarn to the back of the stitches, insert the right hand needle into the front of the stitch on the left hand needle, and push the right hand needle towards the back. Loop the working yarn around the point of the right hand needle, and pull it through the loop of the existing stitch. Again, there's videos on the site linked above, and I've put some step-by-step photos on this instructable too. When using knit stitch, you should see rows of "V" or "N" shapes, depending on how you look at it!
Purl is the counterpart to knit stitch, but, for working in the round (as in this project), it's not as necessary to know - unless you're using some kind of ribbing, or including it in a decorative stitch. To purl, you need to start by bringing the working yarn to the front. This time, the right hand needle slips into the existing left hand needle stitch from the back, and points towards the front of the needles. The yarn loops around the right hand needle again, and the needle pulls it through to the back. When working purl stitch, you'll see smaller "U" shapes in the fabric.