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Attach the yarn to your hook using a slip knot, then work a foundation of chain stitches in multiples of 10.  In other words, the foundation chain can consist of 10 chains, 20 chains, 30 chains, 40 chains, 50 chains, etc. The length of your foundation chain will be the final length of your project. At the end of your foundation chain, work two more chain stitches to serve as a turning chain for your next row. Half double crochet once into the second chain from your hook. When counting chains, do not count the loop currently on your hook. To create the first shell of your first official row, you will need to work a series of treble crochets and half double crochets.  Skip four chains in your foundation. Work nine treble crochets into the fifth chain. Skip another four chains in your foundation. Half double crochet once into the next chain. Repeat the previous step across the full length of your foundation, stopping only once you reach the end of the row.  This completes the first official row. If desired, you can change yarn colors after the end of your first row. Doing so is not necessary, though. Chain three, then work one treble crochet into the front posts of each of the next four stitches. Keep the last loop of each treble crochet on the hook.  After the last treble crochet, yarn over the hook and pull the yarn-over through all the loops on the hook. Chain four again. Work one half double crochet into the next stitch in the previous row. Work a series of treble clusters, chains, and half double crochets across the entire second row, stopping before you work the last five stitches. For each group:  Chain four. Work a front post treble crochet into each of the next four stitches, leaving the last loop on the hook after each one. Half double crochet once, then work another four treble crochets across the next four stitches. Leave the last loop on the hook after each stitch, then yarn over and pull it through the all the loops on your hook after the final stitch. This counts as a nine-stitch shell cluster. Chain four. Work one half double crochet into the front post of the next stitch. Chain four, then work a treble crochet into the front posts of each of the final five stitches in the row, keeping the last loop on the hook for each one.  Yarn over and pull through all the loops after completing the last one. This completes the row. Chain four, then turn the work over. Work four treble crochets into the top of the first cluster, then half double crochet once into the next half double crochet.  Create connecting shells across the entire row, stopping just before the last cluster. For each connecting shell:  Work nine treble crochets into the center of the next cluster. Half double crochet into the next half double crochet.   For the final cluster of the row, work five treble crochets into the top of the cluster. You can change colors at the end of this row or keep going with the color you currently have. At the end of this row, you should also chain one and turn the work over. Work one half double crochet into the first stitch, then work a series of nine-stitch cluster shells across the rest of the row until you reach the end and finish the row.  For each group:  Chain four. Work a nine-stitch shell cluster over the next nine stitches, following the same procedure used to make the nine-stitch shell clusters in your second row. Chain four. Work one half double crochet into the next stitch.   At the very end of the row, chain one and turn the work over. At the start of the fifth row, half double crochet into the first half double crochet stitch. Work across the rest of the row using a series of treble crochets and half double crochets.  For each connecting shell:  Work nine treble crochets into the center of the first cluster. Half double crochet into the next half double crochet.   Continue until you reach the end of the row. If desired, change colors at the end of this row. You've completed a full set of Bavarian crochet at this point. Repeat rows two, three, four, and five until the project reaches your desired width. If you're changing colors, do so at the end of each odd numbered row. When your project is finished, cut the yarn, leaving a tail 2 to 4 inches (5 to 10 cm) long. Pull this tail through the loop on your hook to fasten off and finish the work. Weave the secured tail into the back of the work to hide it.

Summary:
Work a foundation chain. Half double crochet at the start of the next row. Create the first shell. Work additional shells across the row. Front post treble crochet at the start of the next row. Create treble clusters along the entire row. Work a partial cluster at the end of the row. Work treble clusters and half double crochets across the third row. Create nine-stitch cluster shells across the fourth row. Connect the shells across the fifth row. Repeat as needed. Fasten off.