Preheat oven to moderately hot 375°F (190°C) (gas mark 5). Prepare your baking sheet with silpat or parchment paper.
Melt butter in a medium saucepan, then remove from the heat.
To the melted butter add oats, sugar, flour, corn syrup, milk, vanilla, and salt. Mix well. Drop a tablespoon full, three inches (75 mm) apart, onto your prepared baking sheet. Flatten slightly with the back of your tablespoon, or use a spatula.
Bake in preheated oven for 6-8 minutes, until cookies are golden brown. Cool completely on the baking sheets.
While the cookies are cooling melt your chocolate until smooth either in the microwave (1 ½ minutes), or stovetop (in a double boiler, or a bowl that fits atop a saucepan filled with a bit of water, being sure the water doesn't touch the bottom of the bowl).
Peel the cookies from the silpat or parchment and place face down on a wire rack set over a sheet of wax/parchment paper (to keep counters clean).
Spread a tablespoon of chocolate on the bottom/flat side of your cookie, sandwiching another (flat end) cookie atop the chocolate.
This recipe will make about 2 ½ - 3 dozen sandwiched Florentine cookies. You can also choose not to sandwich yours, in which case, drizzle the tops with chocolate (over your wax paper).