Preheat oven to 350°F.
Make the crust: In a medium size bowl mix together flour, brown sugar, and salt. Grate the frozen butter using a box grater and add the butter to the brown sugar and flour. Break up any larger shreds of butter into small pea sized pieces. Combine until mixture resumes coarse crumbs.
1 1/2 cups all-purpose flour, 1 cup light brown sugar, packed, 1/2 tsp. salt, 12 Tbsp. unsalted butter, frozen
Evenly press the crumb mixture into the bottom of a 9x13 baking pan. (You can line with parchment paper first if you prefer). Bake for 15 minutes.
Combine the oats and coconut and pour over the partially baked crust.
3/4 cup quick 1-minute oats, 3/4 cup shredded coconut
Stir together the sweetened condensed milk and vanilla extract and pour over the oats and coconut, being sure to get all along the edges of the pan too.
14 oz. can sweetened condensed milk (1 1/3 cups), 1 Tbsp. vanilla extract
Bake for ~25 minutes or until the filling is set. Cool for 10 minutes.
Meanwhile, melt caramels and milk in saucepan. Whisk and cook over medium-low heat until smooth and melted then pour on top. Sprinkle the top with chocolate chips and flaky sea salt. Cool completely and then cut into bars.
40 vanilla caramels (2, 4.51 oz. bags), 1/4 cup whole milk, 1 cup milk chocolate chips, flaky sea salt