Logic Masters Deutschland e.V.

Normal Sudoku rules apply.
Place the digits 1-9 so that they do not repeat in any row, column, or 3x3 box.

5's live in Dutch Flats
All 5's in the grid must have a '1' directly above it or a '9' directly below it. It may have both, but it doesn't need both.

Double Sandwich Sums
Digits 1, 5, and 9 are crusts. An outside clue gives the sum of the digits sandwiched between the two closest crusts to the clue in its row or column..

To play this puzzle please click here: Play CTC

Previous puzzles in the Dutch Flat Mates series:
Incredibly this is now the 27th puzzle in the series and we haven't missed a single week since the first puzzle in October. Thank you to anyone who has played, and for all the kind comments on the puzzles. We have a few constraints/ideas lined up, and would love to complete a full year.
Any constraint suggestions would be appreciated in the comments.

• Classic
• Thermometers
• German Whispers
• Region Sum Lines
• Sandwich Sums
• Little Killer
• Kropki
• Zipper Lines
• Renban - By GoodCity
• Nabner - By GoodCity
• Skyscrapers - By GoodCity
• Dutch Whispers
• Killer Cages
• Arrows
• Ten Lines
• 159 and Even - By GoodCity
• Friendly Cells
• Quads
• Silent Killer - By GoodCity
• XV and Equality
• X-Sums
• Numbered Rooms - By GoodCity
• Diagonal X-Sums
• Yin Yang (Neighborhoods) - By Palpot
• Hit Points
• XY Difference - By GoodCity

Hint 1 - Where to start

The 30 clues are maxed, and you know it's the nearest sandwich that has to be maxed.

The positions of the crusts in Row 2 are now forced, and you can make use of Dutch Flat Mate knowledge with crust knowledge to make great progress in the puzzle.

If in doubt, recheck unused clues. I tend to use the pen tool when solving puzzles like this, to put a little 'green' or 'red' 'X' next to clues I have or haven't used.

This Weeks Puzzle