Preventing matcha deposits
Matcha doesn't dissolve. 

It is very finely ground to be suspended in water after very vigorous whisking when the preparation is done the traditional way. 

A few tips for your matcha latte:


Use good, high quality matcha. High quality matcha is bright green and a very fine powder (almost like confectioner's sugar or cornstarch) - this helps keeping it suspended in liquid
Whisk very vigorously with the appropriate tools. Traditional tea ceremony uses a bamboo whisk with a lot of room in the bowl to make sure the tea is very well suspended and aerated, and the fork is not the best tool for that. Use a fouet and prepare in a bowl or, if possible, use a blender (a bullet blender or immersion blender would work for small quantities). If all things fail, even a nutritional supplement shaker (the one that has a wire ball inside to help dissolve whey) would be more effective.